CSEC Chemistry Concise Revision Course PDF

~ Collins CONCISE REVISION COURSE ® emlst ,- Anne lindale Collins CONCISE REVISION COURSE ® emlsf " Anne lindale Collins HarperColiins Publishers Ltd The News Building I London Bridge Stree...

~ Collins CONCISE REVISION COURSE ® emlst ,- Anne lindale Collins CONCISE REVISION COURSE ® emlsf " Anne lindale Collins HarperColiins Publishers Ltd The News Building I London Bridge Street London SE I 9GF First edition 2016 1098765432 © HarperColiins Publishers limited 2016 ISBN 978-0-00-815788-3 Collins® is a registered trademark of HarperCollins Publishers limited Concise Revision Course: CSEC® Chemistry is an independent publication and has not been authorised, sponsored or otherwise approved by CXC®, CSEC®is a registered trade mark of the Caribbean Examinations Council (CXC). www.collins.co.uklcaribbeanschools A catalogue record for this book is available from the British Library. Typeset by QBS Printed in Italy by Grafica Veneta S.p.A. All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission in writing of the Publisher. This book is sold subject to the conditions that it shall not, by way of trade or otherwise, be lent, re-sold, hired out or otherwise circulated without the Publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser. If any copyright holders have been omitted. please contact the Publisher who will make the necessary arrangements at the first opportunity. Author:Anne Tindale Publisher: Elaine Higgleton Commissioning Editor: Peter Dennis Managing Editor: Sarah Thomas Copy Editor: Delphine Phin Editor:Aidan Gill Proofreader:Tim Jackson Artwork: QBS Cover: Kevin Robbins and Gordon MacGilp Acknowledgements The publishers would like to thank the following for permission to use their photos in this book: p72:Anne Tindale; p89:Anne Tindale; pi 03:Andre Nitsievsky/Shutterstock; p 134: Photo smileJShutterstock; p I461:Toa55/Shutterstock; p 146r: Lodimup/Shutterstock; p 1671: PChStudiosJShutterstock; p 167r: Mark Sykes/Science Photo library; p 178: Mikadun/Shutterstock; p I 841:ThamKC/Shutterstock; p 184r: Mexrix/Shutterstock; p 186:Anne Tindale; p 187:Anne Tindale Contents The pathway to success v Reversible reactions 50 Revision questions 50 1 The states of matter 1 The particulate theory of matter 1 8 The mole concept 51 Evidence to support the particulate Relative atomic, molecular and formula masses 51 theory of matter The mole 52 Uses of osmosis 3 The mole and mass 52 Types of particles that make up matter 3 The mole and number of particles 53 The three states of matter 4 The mole, mass and number of particles 54 Changing state 4 The mole and volumes of gases 55 Revision questions 6 The mole, mass, number of particles and gas volume 55 2 Pure substances, mixtures and Revision questions 56 separations 7 The mole and chemical formulae 56 Pure substances 7 Percentage composition 58 Mixtures 9 The mole and solutions 58 Solutions, suspensions and colloids 9 Revision questions 59 Solubility 11 The mole and chemical reactions 60 Separating the components of mixtures 12 Revision quest-ions 63 The extraction of sucrose from sugar cane 16 9 Acids, baS1?S and salts 64 Revision questions 17 Acids 64 3 Atomic structure 18 Bases 67 Subatomic particles 18 Distinguishing between acids and alkalis 68 The arrangement of subatomic particles The strength of acids and alkalis 68 in an atom 19 Amphoteric oxides and hydroxides 69 Isotopes 20 Classification of oxides 70 Revision questions 23 Revision questions 70 Salts 71 4 The periodic table and periodicity 24 Methods used to prepare salts 72 The historical development of Salts in everyday life 76 the periodic table 24 Neutralisation reactions 77 The modern periodic table 24 Volumetric analysis 78 Trends in Group 11- the alkaline earth metals 26 Revision questions 81 Trends in Group VII - the halogens 27 10 Oxidation-reduction reactions 82 Trends in Period 3 28 Revision questions 29 Oxidation-reduction reactions in terms of electrons 82 5 Structure and bonding 30 Oxidation number or oxidation state 82 Chemical formulae 30 Oxidation-reduction reactions in Ionic bonding 32 terms of oxidation number 84 Covalent bonding 36 Using oxidation numbers to recognise redox Drawing dot and cross bonding diagrams 37 reactions 85 Metallic bonding 39 Oxidising and reducing agents 86 The structure and properties of solids 39 Tests for oxidising and reducing agents 88 Revision questions 43 Oxidation-reduction reactions in everyday activities 89 6 Chemica l equations 44 Revision question s 90 Writing balanced equations 44 11 Electrochemistry 91 Ionic equations 47 Revision questions 48 Predicting reactions using the electrochemical series of metals 91 7 Types of chemical reaction 49 Predicting reactions using the electrochemical Synthesis reactions 49 series of non-metals 92 Decomposition reactions 49 Electrical conduction 92 Single displacement reactions 49 Electrolysis 93 Ionic precipitation reactions 49 Electrolysis of molten electrolytes 95 Oxidation-reduction reactions 50 Electrolysis of aqueous electrolytes 95 Neutralisation reactions 50 Revision questions 99 Contents iii  Quantitative electrolysis 100 18 Characteristics of metals 155 Industrial applications of electrolysis 102 Physical properties of metals 155 Revision questions 105 Chemical properties of metals 155 12 Rates of reaction 106 Reactions of metal compounds 156 Revision questions 157 Measuring rates of reaction 106 The collision theory for chemical reactions 106 19 The reactivity, extraction and Rate curves for reactions 107 uses of metals 158 Factors that affect rates of reaction 107 The effect of changing different factors The reactivity series of metals 158 on rate curves 109 The extraction of metals from their ores 159 Revision questions 110 Extraction of aluminium 160 Extraction of iron 160 13 Energetics 111 Uses of metals 162 Exothermic and endothermic reactions 111 Alloys and uses of alloys 162 Breaking and forming bonds during reactions 111 Revision questions 164 Enthalpy changes during reactions 111 20 Impact of metals on living Energy profile diagrams 112 Calculating enthalpy changes 113 systems and the environment 165 Revision questions 116 Corrosion of metals 165 The importance of metals and Exam-style questions - Chapters 1 to 13 117 their compounds 14 Organic chemistry - an introduction 123 in living organisms 165 Harmful effects of metals and Bonding in organic compounds 123 The structure of organic molecules 124 their compounds 166 Formulae of organic compounds 124 Revision questions 167 Homologous series 125 21 Non-metals 168 Structural isomerism 126 The alkanes: CnH2n+2 128 Physical properties of non-metals 168 129 Chemical properties of non-metals 169 The alkenes: CnHzn Behaviour of non-metals as oxidising and Alcohols: CoH'o>,OH or R- OH 131 132 reducing agents 170 Alkanoic acids: CoH' o.,COOH or R-COOH Revision questions 132 Laboratory prepa·ration of gases 170 Uses of carbon dioxide and oxygen 172 15 Sources of hydrocarbon compounds 134 Uses of non-metals and their compounds 173 Harmful effects of non-metals and Natural sources of hydrocarbons 134 Fractional distillation of crude oil 134 their compounds 176 Cracking hydrocarbons 135 Revision questions 178 Revision questions n6 22 Water 179 16 Reactions of carbon compounds 137 The unique properties of water 179 137 Consequences of water's solvent properties 180 The alkanes: C n H2n +2 138 Treatment of water for domestic use 181 The alkenes: CoH,o Distinguishing between an alkane Revision questions 182 and an alkene 139 23 Green Chemistry 183 Uses of alkanes and alkenes 140 Revision questions 141 The twelve principles of Green Chemistry 183 141 Revision questions 184 Alcohols: CoH'o>,OH or R-OH Alkanoic acids: C" H,,,., COOH or R- COOH 143 24 Qualitative analysis 185 Esters: CnHzn+1COOCxH2x+l or R-COO-R' 143 145 Identifying cations 185 Soapy and soapless detergents Revision questions 147 Identifying anions 188 Identifying gases 190 17 Po lymers 148 Revision questions 191 Formation of polymers 148 Exam-style questions - Chapters 18 to 24 193 Uses of polymers 150 Appendix - The Periodic Table 196 Impact of synthetic polymers (plastics) , on the environment 150 Revision questions 151 Index 197 Exam-style questions - Chapters 14 to 17 152 Contents The pathway to success About this book This book has been written primarily as a revision course for students studying for the CSEC· Chemistry examination. The facts are presented concisely using a variety of fo rmats which makes them easy to understand and learn. Key words are highlighted in bold type and important definitions which must be learnt are written in italics and highlighted in colour. Annotated diagrams and tables have been used wherever possible and worked examples have been included where appropriate. Questions to help test knowledge and understanding, and provide practice for the actual examination, are included throughout the book. Th e following sections provide valuable information on the format of the CSEC· examination, how to revise successfully, successful examination technique, key terms used on examination papers and School-Based Assessment. The CSEC® Chemistry syllabus and this book The CSEC· Chemistry syllabus is available online at http://cxc-store.com. You are strongly advised to read through this syllabus carefully since it provides detailed information on the specific objectives of each topic of the course, School-Based Assessment (SBA) and the format of the CSEC· Examination. Each chapter in this book covers a particular topic in the syllabus. Chapters 1 to 13 cover topics in Section A, Principles of Chemistry Chapters 14 to 17 cover topics in Section B, Organic Chemistry Chapters 18 to 24 cover topics in Section C, Inorganic Chemistry At the end of each chapter, or section within a chapter, you will find a selection of revision questions. These questions test your knowledge and understanding of the topic covered in the chapter or section. At the end Chapters 13, 17 and 24 you will find a selection of exam-style questions which also test how you apply the knowledge you have gained and help prepare you to answer the different styles of questions that you will encounter in your CSEC· examination. You will find the answers to all these questions online at www.collins.co.uk/caribbeanschools. The format of the CSEC® Chemistry examination The examination consists of two papers and your performance is evaluated using the following three profiles: Knowledge and comprehension Use of knowledge Experimental skills The pathway to success V Paper 01 (1 % hours) Paper 01 consists of 60 multiple choice questions. Each question is worth 1 mark. Four choices of answer are provided for each question of which one is correct. Make sure you read each question thoroughly; some questions may ask which answer is incorrect. If you don't know the answer, try to work it out by eliminating the incorrect answers. Never leave a question unanswered. Paper 02 (2 Y, hours) Paper 02 is divided into Sections A and B, and consists of six compulsory questions, each divided into several parts. Take time to read the entire paper before beginning to answer any of the questions. Section A consists of three compulsory structured questions whose parts require short answers, usually a word, a sentence or a short paragraph. The answers are to be written in spaces provided on the paper. These spaces indicate the length of answer required and answers should be restricted to them. Question 1 is a data-analysis question which is worth 25 marks. The first part usually asks you to take readings from a measuring instrument, such as a set of thermometers, and record these readings in a table. You may then be asked to draw a graph using the information in the table and may be asked questions about the graph or be asked to perform certain calculations. The second part will possibly test your knowledge of tests to identify cations, anions and gases, and there may be a third part which tests your planning and designing skills. Questions 2 and 3 are each worth 15 marks. They usually begin with some kind of stimulus material, such as a diagram or a table, which you will be asked questions about. Section B consists of three compulsory extended-response questions, each worth 15 marks. These questions require a greater element of essay writing in their answers than those in Section A. The marks allocated for the different parts of each question are clearly given. A total of 100 marks is available for Paper 02 and the time allowed is 150 minutes. You should allow about 35 minutes for the data-analysis question worth 25 marks and allow about 20 minutes for each of the other questions. This will allow you time to read the paper fully before you begin and time to check over your answers when you have finished. Successful revision The following should provide a guide for successful revision. Begin your revision early. You should start your revision at least two months before the examination and should plan a revision timetable to cover this period. Plan to revise in the evenings when you don't have much homework, at weekends, during the Easter vacation and during study leave. , The oathwav to surp~  When you have a full day available for revision, consider the day as three sessions of about three to four hours each, morning, afternoon and evening. Study during two of these sessions only, do something non-academic and relaxing during the third. Read through the topic you plan to learn to make sure you understand it before starting to learn it; understanding is a lot safer than thoughtless learning. Try to understand and learn one topic in each revision session, more if topics are sho rt and fewer if topics are long. Revise every topic in the syllabus. Do not pick and choose topics since all questions on your exam paper are compulsory. learn the topics in order. When you have learnt all topics once, go back to the first topic and begin again. Try to cover each topic several times. Revise in a quiet location without any form of distraction. Sit up to revise, preferably at a table. Do not sit in a comfy chair or lie on a bed where you can easily fall asleep. Obtain copies of past CSEC® Chemistry examination papers and use them to practise answering exam-style questions, starting with the most rec;e,iit papers. These can be purchased online from the CXC Store.. You can use a variety of different methods to learn your wink. Chose which ones work best for you. Read the topic several times, then close the book and try to write down the main points. Do not try to memorise your work word for word since work learnt by heart is not usually understood and most questions test understanding, not just the ability to repeat facts. Summarise the main points of each topic on flash cards and use these to hel p you study. Draw simple diagrams with annotations, flow charts and spider diagrams to summarise topics in visual ways which are easy to learn. Practise drawing and labelling simple line diagrams of apparatus you have encountered. You may be asked to reproduce these, e.g. the apparatus used for fractional distillation. Practise writing equations. Do not try to learn equations by heart; instead, understand and learn how to write and balance them. For example, if you learn that a carbonate reacts with an acid to form a salt, carbon dioxide and water, you can write the equation for any carbonate reacting with any acid. Use memory aids such as: - acronyms, e.g. Oil RIG for oxidation and reduction in terms of electrons; oxidation is loss, reduction is gain. - mnemonics, e.g. 'Peter sometimes collects money at zoos in london helping crazy monkeys and silly giraffes' for the order of metals in the reactivity series; potassium, sodium, calcium, magnesium, aluminium, zinc, iron, (hydrogen), copper, mercury, silver, gold. - associations between words, e.g. anions - negative (therefore cations must be positive). Test yourself using the questions throughout this book and others from past CSEC®examination papers. The pathway to success vii Successful examination technique o Read the instructions at the start of each paper very carefully and do precisely what they requ ire. o Read through the entire paper before you begin to answer any of the questions. o Read each question at least twice before beginning your answer to ensure you understand what it asks. o Underline the important words in each question to help you answer precisely what the question is asking. oRe-read the question when you are part way through your answer to check that you are answering what it asks. o Give precise and factual answers. You will not get marks for information which is 'padded out' or irrelevant. The number of marks awarded for each answer indicates how long and detailed it should be. o Use correct scientific terminology throughout your answers. o Balance all chemical equations and ensu re that you give the correct state symbols, especially in ionic equations. o Show all working and give clear statements when answering questions that require calculations. o Give every numerical answer the appropriate unit using the proper abbreviation/ symbol e.g. cm ' , g, 0c. o If a question asks you to give a specific number of points, use bullets to make each separate point clear. o If you are asked to give similarities and differences, you must make it clear which points you are proposing as similarities and which points as differences. The same applies if you are asked to give advantages and disadvantages. o Watch the time as you work. Know the time available for each question and stick to it. o Check over your answers when you have completed all the questions, especially those requiring calculations. o Remain in the examination room until the end of the examination and recheck your answers again if you have time to ensure you have done your very best. Never leave the examination room early. Some key terms used on examination papers Account for: provide reasons for the information given. Calculate: give a numerical so lu tion which includes all relevant working. Compare: give similarities and differences. Construct: draw a graph or table using data provided or obtained. Contrast: give differences. The pathway to success Deduce: use data provided or obtained to arrive at a conclusion. Define: state concisely the meaning of a word or term. Describe: provid e a detailed account which includes all relevant information. Determine: find a solution using the information provided, usually by performing a ca lculation. Discuss: provide a balanced argument which considers points both for and against. Distinguish between or among: give differences. Evaluate: determine the significance or worth of the point in question. Explain: give a clear, detailed account which makes given information easy to understand and provides reasons for the information. Illustrate: make the answer clearer by including examples or diagrams. Justify: provide adequate grounds for your reasoning. Outline: write an account which includes the main points only. Predict: use information provided to arrive at a likely conclusion or suggest a possible outcome. Relate: show connections between different sets of information or data. State or list: give brief, precise facts without detail. Suggest: put forward an idea. Tabulate: construct a table to show information or data which has been given or obtained. Drawing tables and graphs Tables Tables can be used to record numerical data, observations and inferences. When drawing a table: o Neatly enclose the table and draw vertical and horizontal lines to separate columns and rows. o When drawing numerical tables, give th e correct column headings which state the physical quantities measured and give th e correct units using proper abbreviations/ symbols, e.g. cm J , g, aC. o Give the appropriate number of decimal places when recording numerical data. o When drawing non-numerical tables, give the correct column headings and all observations. o Give the table an appropriate title which must include reference to the responding variable and the manipulated variable. The pathway to success ix Graphs Graphs are used to display numerical data. When drawing a graph: o Plot the manipulated variable on the x-axis and the responding variable on the y-axis. o Choose appropriate scales which are easy to work with and use as much of the graph paper as possible. o Enter numbers along the axes and label each axis, including relevant units, e.g. cm 3, g, oc. o Use a small dot surrounded by a small circle to plot each point. o Plot each point accurately. o Drawa smooth curve or straight line of best fit which need not necessarily pass through all the points. o Give the graph an appropriate title which must include reference to the responding variable and the manipulated variable. School-Based Assessment (SBA) School-Based Assessment (SBA) is an integral part of your CSEC· examination. It assesses you in the Experimental Skills and Analysis and Interpretation involved in laboratory and field work, and is worth 20% of you r final examination mark. o The assessments are carried out in your school by your teacher during Terms 1 to 5 of your two-year programme. o The assessments are carried out during normal practical classes and not under examination conditions. You have every opportunity to gain a high score in each assessment if you make a consistent effort throughout you r two-year programme. o Assessments will be made of the following four skills: Manipulation and Measurement Observation, Recording and Reporting Planning and Designing Analysis and Interpretation As part of your SBA, you will also carry out an Investigative Project during the second year of your two-year programme. This project assesses your Planning and Designing, and Analysis and Interpretation skills. If you are studying two or three of the single science subjects, Biology, Chemistry and Physics, you may elect to carry out ONE investigation only from anyone of these subjects. You will be required to keep a practical workbook in which you record all of your practical work and this may then be moderated externally by Cxc. The pathway to success 1 The states of matter Chemistry is the study of the composition, structure, properti es and reaction s of matter. Everything around us is made of matter. Malter /s anything thai has volume and mcp.;s. All matter is made of particles and can exist in three different states: The solid state The liquid state The gaseous state The particulate theory of matter There are four main ideas behind the particulate theory of matter: A ll matter is composed of particles. The particles are in constant motion and temperature affects their speed of motion. The particles have empty spaces between them. The particles have forces of attraction betwee n them. Evidence to support the particulate theory of matter The processes of diffusion and osmosis provide evidence to suppo rt the fact that all matter is made of particles. Diffusion D iffusion is the net mon.' tnenl of particles from a region of hiR/H'f concentration to d region of lo\\'er wneenlrallOn, unlitlh" pdrlic/cs are evenly d"lniJuleci. Particl es in gases and liquids are capable of diffusing. Exa mple 1 When pieces of cotton wool soa ked in concentrated ammonia so lution and concentrated hydrochloriC acid are placed simultaneously at opposite ends of a glass tub e, a white ring of ammonium chloride form s inside the tub e. Ammonia so lution gives off ammonia gas and hydroch loriC acid gives off hydrogen chloride gas. The particles of the gases diffuse throu gh the air inside the tube, co llide and react to form amm onium chloride: ammonia + hydrogen ch loride ammonium chloride NH,(g) + HCI(g) NH, CI(s) Ammonia particles diffuse faster than hydrogen chloride particl es, so the particles co llide and react close r to the source of the hydrogen chloride particles. 1 ammonia particles 2 hydrogen chloride diffuse very quickly particles diffuse quickly along the lube along the tube cotion wool soaked in iI., ':,-"\C ~ ~ -t ~ { cotion wool soaked in conetra t~d ~ ~.... concentrated ammOnia _ ~ _ ,, _ hydrochloric solution I acid 3 ammonia and hydrogen chloride particles collide, react and form a ring of white ammonium chloride Figure 1.1 Gases diffus e 1 The states of matter Example 2 When a purple potassium manganate(VII) crystal is placed in water, it dissolves to produce a uniformly purpl e solution. The particles making up the crystal separate from each oth er and diffuse through the spaces between the water particles until they are even ly distributed. purple potassium manganate(VlI) solution gradually forms 1 water particles move randomly and have small spaces 3 crystal particles between gradually separate from each other and diffuse into the spaces between the water water particles 2 crystal particles potassium packed tightly manganate(VII) -+-- together crystal before dissolving during dissolving Figure 1.2 Crystals dissolve Osmosis Osmosis is the movement of water molecules through a differentially permeable membrane from a solution containing a lot of wa ter molecules, e.g. a dilute solution (or \valer), Lo a solution containing fewer water molecules, e.g. a concentrated soluUon. Example 1 When a dilute sucrose solution is separated from a conce ntrated suc ros e solution by a differentially permeable membrane, water molecules move through the membrane from the dilute solution into the concentrated solution, but the sucrose molecules cannot move in the other direction. The volume of the concentrated solution increases and the volume of the dilute so lution decreases. glass tube - -- ----1 o 3 the level 01 the concentrated o solution rises due to its increased volume , differentially permeable membrane - has minute 2 sucrose particles pOres which only allow try to diffuse through the water particles through membrane into the dilute solution. but they are unable to pass through the pores o 1 water particles diffuse o· through the pores in the membrane into the concentrated solution causing its volume to concentrated Increase sucrose solution Figure 1.3 'Osmosis explained 1 Concise Revision Course: CSEC· Chemistry Exa mpl e 2 The membranes of living cells are differentially permeable and the cytoplasm inside the cells contains abo ut 80% water. When a strip of living tissue (such as paw-paw) is placed in water, water molecules move into the cells by osmosis. Each cell swells slightly, and the strip increases in length and becomes rigid. When the strip is placed in a concentrated sodium chloride solution, water molecules move out of the cells by osmosis. Each cell shrinks slightly, and the strip decreases in length and becomes softer. Uses of osmosis To control garden pests Slugs and snails are garden pests, whose skin is differentially permeable and always moist. When salt (sodium chloride) is sprinkled on slugs and snails, it dissolves in the moisture around their bodies forming a concentrated solution. Water inside their bodies then moves out by osmosis and into the solution. The slugs and snails die from dehydration if their bodies lose more water than they can tolerate. To preserve food Salt and sugar are used to preserve foods such as meat, fish and fruit. They both work in the same way: They draw water out of the cells of the food by osmosis. This prevents the food from decaying because there is no water available in the cells for the chemical reactions which cause the decay. They draw water out of microorganisms (bacteria and fungi ) by osmosis. This prevents the food from decaying because it inhibits the growth of the microorganisms that cause the decay. Types of particles that make up matter There are three different typ es of particles that make up matter: Atoms Atoms are the smallest units of a chemical element which have all the characteristics of the element. For example, iron is made of iron atoms, Fe (see p. 7). Molecules Molecules are groups of two or more atoms bonded together and which can exist on their own. Molecules may be made up of atoms of the same kind, e.g. hydrogen molecules, H" are mad e up of hydrogen atoms, H. Molecules may also be made up of atoms of different kind s, e.g. carbon dioxide molecules, CO" are made up of carbon atoms, C, and oxygen atoms, ° (see p. 36). Ions Ions are electrically charged particles. Ions may be formed from a single atom, e.g. the potassium ion, K'. They may also be formed from groups of two or more atoms bonded together, e.g. the nitrate ion, NO,' (see p. 34). 1 The states of matter The three states of matter The particulate theory of matter helps explain the physical properties of matter and th e differences between the three states. Table 1.1 Comparing the three states of matter 'I' Shape Fixed. Takes the shape of the Takes the shape of the entire part of the container it is container it is in. in. The surface is always horizontal. Volume Fixed. Fixed. Variable - it expands to fill the container it is in. Density Usually high. Usually lower than solids. Low. Compressibility Difficult to Can be compressed Very easy to compress. compress. very slightly by applying pressu reo Arrangement of Packed closely Have small spaces Have large spaces between particles together, usually between and are and are randomly arranged: in a regular way: randomly arranged: i \ Forces of attraction Strong. Weaker than those Very weak. between the particles between the particles in a solid. Energy possessed by Possess very Possess more kinetic Possess large amounts of the particles small amounts of energy that the particles kinetic energy. kinetic energy. in a solid. Movement of the Vibrate in their Move slowly past each Move around freely and particles fixed position. other. rapidly. Changing state Matter can exist in any of the three states depending on its temperature. It can change from one state to another by heating or cooling, as this causes a change in the kinetic energy and arrangement of the particles: When a so lid is heated, it usually changes state to a liquid and then to a gas. This occurs because the particles gain kinetic energy, move increasingly faster and further apart, and the forces of attraction between them become increasingly weaker. When a gas is cooled, it usually changes state to a liquid and then to a solid. This occurs because the particles lose kinetic energy, move more and more slowly and closer together, and the forces of attraction between them become increasingly stronger. 1 Concise Revision Course: CSEC· Chemistry  add heat evaporation/ melting boiling SOLID LIQUID GAS I freezing condensation I sublimation deposItion remove heat Figure 1.4 Changing state Evaporation and boiling are different in the following ways: Evaporation can take place at any temperature, whereas boiling occurs at a specific temperature. Evaporation takes place at the surface of the liquid only, whereas boiling takes place throughout the liquid. Substances which sublimate (or sublime) change directly from a solidi o a gas. The reverse process in which a gas changes directly to a solid is called deposition. Examples of substances that sublimate include carbon dioxide ('dry ice'), iodine and naphthalene (moth balls). Heating and cooling curves A heating curve is drawn when the temperature of a solid is measured at intervals as it is heated and changes state to a liquid and then to a gas, and the temperature is then plotted against time. A cooling curve is drawn when the temperature of a gas is measured at intervals as it is cooled and changes state to a liquid and then to a solid, and the temperature is then plotted against time. gas liquid and gas ,---"...:.c..==J.......-- boiling point - temperature stays constant until the liquid has all boiled (or the gas has all liquid condensed) solid and liquid ,-----'---'-~H H H- C ~ /C-C, H / \ Ii C- H H HH Catenation is th e ability of carbon atoms to bond covalentl y with other carbon atoms to form chains and rings of carbon atoms. The structure of organic molecules The simplest organic molecules can be thought of as being composed of two parts: o The hydrocarbon part composed of only carbon and hydrogen atom s. o The functional group (or groups), composed of a particular atom, group of atoms, or bond between adjacent carbon atoms, such as - OH, - COOH (see Table 14.2 on p. 126). The chemical properties of a compound are determined by the reactions of the functional group (or groups) present. Formulae of organic compounds The formulae of organic compound s can be written in different ways. The most common ways are: o The molecular formula. This shows the total number of atoms of each element present in one molecule of the compound. o The fully displayed structural formula. This shows how the atoms are bonded in one molecule in a two-dimensional diagramatic form, using a line to represent each covalent bond. o The condensed structural formula. Thi s shows the sequence and arrangement of the atoms in one molecule so that the position of attachment and nature of each functional group is shown without drawing the molecule. This can be condensed further to show the total number of carbon atoms and total number of hydrogen atoms in the hydrocarbon part of the molecule. Example Propanoic acid The functional group of propanoic acid is -COOH. o Its molecular formula is C]H,O , o Its fully displayed structural formula is H H I I ",0 H-C-C-C I H I H ' O-H 14 Concise Revision Course: CSEC· Chemistry o Its condensed structural formula is CH,CH,COOH This can be condensed further to C, H,COOH Ho mologous series organic com po und s can be classified into groups known as homologous series. These are based on Ih e fu nctional group w hich th ey contain. Each homologo us series can be represent ed by a general formula, for example, the general formula of the alkane series is CoH,o.,. A homologous series is a group of organ ic compounds which all possess the same functional group and can be represented by th e sa m e general formula. The characterist ics of a homologous series Each homologous series has the fo llow ing characteristics: o Members of a series all have the sa me functional group. o Membe rs of a series can all be repre sented by the same general formula. o The molecular formula of each member of a se ri es differs from the member directly before it or directly after it by CH, and, therefore, by a relative molecular mass.pf 14. o Membe rs of a series can all be prepared using the same ge nera l method. o Membe rs of a seri es all possess simil ar chemical properties. As th e mo lar mass (num ber of carbon atoms per molecul e) increases, the reacti vity decreases. o Mem bers of a se ri es show a gradual change in their physical properties as the number of ca rbon atoms per molecule increases. Generally, as molar mass in creases, th e melting po int, boiling point and density increase. How to name the straight chain members of a homologous series Straight chain members of a homologo us series have a nam e co nsisti ng of two parts: o The first part, or prefix, w hich depends on the total number of carbon atoms in one mo lecule. Table 14.1 Prefixes used to name organic compo unds 1 meth· 2 eth- 3 prop- 4 but- S pent· 6 hex- o The seco nd part, which d epends on th e functional group present in the compound (see Table 14.2, p. 126). 14 Organic chemistry - an introd uction Table 14.2 The four main homologous series :... Alkane Cn H2n+ 2 carbon-carbon prefix +.. propane H H H single bond ane (prop + I I I H-C-C-C-H ane) I I I I I H H H -C-C - I I CH JCH 2CH) or C3HS Alkene Cn H2f1 carbon - carbon prefix + propene H H H double bond ene (prop + I I / H-C - C=C ene) I "- H "- c=c / H / "- CH3CH = CH z or CJH6 Alcohol or Cn H 2n + 1OH hydroxyl group prefix + propanol H H H alkanol anol (prop + I I I -O-H H-C-C-C-O-H (- OH) anol) I I I H H H CHJCH2CHp H or C)HpH Alkanoic acid CoH'o" COOH carboxyl group prefix propanoic H H I I 1'0 or carboxylic /0 + anoic acid H-C-C - C acid -c" acid (prop + I I "- O- H "- O- H H H anoic acid ) CH)CH 2COOH or (- COGH) C2HsCOOH Structural isomerism Organic compounds can have the same molecular formula but different structural formulae because their atoms are bonded different ly. These are cal led structural isomers. Structural isomers are organic compounds which have the same molecular formula but different structural formulae. Structural isomerism is the occurrence of two or more organic compounds with the same molecular formula but different structural formulae. Each different structural isomer has a different name, and if they contain the same functional group, they belong to the same homologous series. Structural isomers of straight chain molecules can be formed in two ways: By the chain of carbon atoms becoming branched. By the position of the functional group changing. Isomers formed by branching Carbon chains can have side branches composed of one or more carbon atoms. For this to happen, the molecules must have four or more carbon atoms. 14 Concise Revision Course: CSEC' Chemistry Exam p le Isomers of C.H' 4 C H has five iso m e rs, three are given belo w : 6 " H H I I H-C-H H-C - H H H H H H H H H H I H H H I H I I I I I I I I I I I I I H- C-C-C-C-C-C-H H-C-C-C-C-C-H H-C-C-C-C-H I H H H H I I I I H H I I I H H H H H I I I I I H I H H I H-C-H I H CH3CHlC H2CH2CH2CH3 CH3C H2CH2CH(CH3ICH3 CH3CH2C(CH3l2CH3 A B C When d rawing th e st ructural fo rmul a o f any o rga ni c compo un d, th e longest contin uous chain o f carbon ato m s mu st always be drawn horizontally and care must b e taken no t to draw be nt versio ns of the stra ight chai n isom e r o r mirro r images of bra nched chain isome rs. To check if two structu res are isom e rs, w rite th e condensed structural formula of each. W hen readin g these fo rmul ae forwa rd s or backwards, i f tw o fo rmulae are th e same, t ~e n th e st ru ct u res are ",!! not iso m e rs. H H I I H-C- H H-C-H H H H H I I I I I H I H I I H H I I H- C-C-C - C- C-H H-C-C-C-C-C-H I I I I I I I I I I H H H H H H H H H H CH3CHlCH2CHlCH2CH3 CH3CH(CH3)CH2CHlCH3 This is a bent version of This is a mirror image of B, A, it is not another isomer It is not another isomer How to name branched chain isomers Side ch ai ns branching off fro m the lo ngest chain o f carbon ato m s are ca lled alkyl groups. They have the gen e ral formula Co H2,. , and are nam ed usin g th e appropriate prefi x with th e endin g '-yl'. Table 14.3 Naming alkyl groups I I - CH3 m eth yl - CH2CH3 or - C, Hs ethyl - CH,CH,CH3 or -C3H, propyl The name o f any b ranched chain m o lecu le has three pa rt s: The first part gives th e number of the carbon atom to w h ich th e al ky l gro up (sid e chain) is attach ed. The second part gives th e name o f th e alkyl g ro up (see Table 14.3 above). The third part gives in fo rm ati on abo ut th e longest continu o us chain o f carbo n ato m s. The number of carbon atoms in thi s chain is indicated usin g the co rrect prefix, and th e homologous series t o whi ch th e compound be longs is indicated usin g th e co rrect ending. 14 Orga nic chem istry - an introd uction Exa mple To determine th e name of the following branched chain isomer of C,H,,: H H H H H I I I I I H-C-C-C - C- C-H I H H H I H I I I H- C-H I H Number the carbon atoms in the longest continuous chain of carbon atoms from the end closest to the alkyl group so that the group is attached to the atom with the lowest possible number: H H H H H I I I I I H-C'- CL CL CL CL H I H H H IH I I I H-C-H I H Name the isomer using the following information: The first part: the alkyl group is attached to carbon atom number 2. The second part: the alkyl group ha s one carbon atom, so it is the methyl group. The third part: the longest continuous carbon chain has five carbon atoms, so its prefix is 'pent-'. The compound has the general formula C"H,"", so it belongs to the alkane series which means its name ends in '-ane'. The isomer is called 2-methylpentane. Isomers formed by changing the position of the functional group A compound is usually drawn so that its functional group is shown at the right hand end of the molecule; however, its position ca n change. This is see n in the alkene and alcohol series (Tables 14.6,14.7 and 14.8, pp. 130 and 131). The alkanes: C n H2n +2 Alkanes contain only single bonds between carbon atoms. Alkanes with four or more carbon atoms show structural isomerism resulting from their ability to form branched chains.. Table 14.4 The first three alkanes. Structural formula H H H H H H I I I I I I and name H-C-H H- C- C-H H-C -C-C -H I I I I I I H H H H H H methane ethane propane 14 Concise Revision Course: CSEC' Chemistry Table 14.5 Th e isomers of alkanes with four, five and six carbon atoms H H H H H H H I I I I I I I H-C-C-C-C-H H-C-C-C-H I I I I I I I H H H H H H H-C-H I H butane 2-methylpropane H I H H H H H H-C-H H H H H I I I H-C-C-C-C-C - H I I I H-C - C- C-C-H I I I H I I H I I I I I I H-C-C-C- H I H I I I ~ I ~ H H H H H H H H- C- H I H-C-H H I H pentane 2-methylbutane '.~ 2,2-dimethylpropane H H H H H H H H H H H H H H H H I I I I I I I I I I I I I I I I H-C-C-C-C-C-C- H H-C-C-C-C-C-H H-C-C-C-C-C-H I I I I I I H H H H H H I H H H I H I I I I H H I H H I I I H-C -H H-C-H I I H H hexane 2-methylpentane 3-methylpentane H H I I H- C- H H-C-H ~ ~ I ~ H I I H H I I H-C -C-C-C- H H-C - C-C-C -H H I I H I H I I I H I H H I H-C-H H-C - H I I H H 2,2-dimethylbutane 2,3-dimethylbutane Note The prefix 'normal' or 'n-' is sometimes used before the name o f the straight chain isomers. For exa mpl e, the straig ht chain isomer of butane is sometimes ca lled normal butane or n-butane. Alkenes co ntain one double bond between two carbon atom s. Their functional gro up is this carbon- carbon double bond: 'c=c / / "- Alkenes with four or more ca rbon atoms show structural isomerism resulting from: A change in position of the carbon-carbon double bond. Thi s bond must always be drawn horizontally. Branching of the molecule. 14 Organic chemistry - an introduction To name unbranched isomers of alkenes, number th e ca rbon atoms in th e longest co ntinuous chain from th e end clo sest to the double bond. Indi ca te th e positi o n of the doubl e bond using th e lowest possible num ber of the carbon atom it is attached to (see Tabl es 14.6 and 14.7). Branched isomers are named followin g th e guide lines given on p. 127, but usin g th e ending '-ene'. Table 14.6 The first three alkenes.. C,H, H , / H H / C= C , H ethene H H I I /H H-C-C=C I H ' H propene H I /H H-C-C=C H H H I I I /H H H H H I I I I ~ I 'H H-C-C-C=C H-C-C =C-C- H H-C-H I H H I ' H I I I H H H but-1-ene but-2-ene 2-methylpropene (or 1-b uten e) (or 2-b utene) Table 14.7 Th e unbranched isomers of p entene and hexene H H H H H H H H H I I I I / H I I I I I H-C-C-C-C=C H-C-C-C=C -C- H I I I ' H I I I H H H H H H pent-1-ene pent-2-ene (o r 1-pentene) (or 2-pentene) HHHHH H HHHHHH HHHHH H I I I I I / I I I I I I I I I I I I H-C-C-C-C-C=C H-C-C-C - C=C-C - H H-C-C-C=C - C-C-H I H H I H H I I 'H I H I H H I I H I H I H I H H I hex-1-ene hex-2-ene hex-3-ene (or 1-hexene) (o r 2-hexene) (or 3-hexene) 14 Concise Revision Course: CSEC· Chemistry Alcohols (or alkanols) have the hydroxyl group (- OH) as their functional group. Al co hols with three or more carbon atoms show structural isomerism resulting from: o A change in position of the hydroxyl (- OH) group. o Branching of th e mo lecul e. To name unbranched isomers of alcohols, number th e carbo n atoms in the longest continuous chain from the end close st to the -O H group. Indicate th e position of the group using the number of the carbon atom it is bonded to (see Table 14.8). Branched isomers are named following the guidelines given on p. 127, but using the ending '-anol'. Table 14.8 Th e unbranched isomers of the first five alcohols I I' I 0 CH,OH H I H-C-O-H I H methanol C, H,OH H H I I H-C - C-O-H I I H H ethanol C, H,OH H H H H H H I I I I I I H-C-C-C-O-H H- C-C-C-H I I I I I I H H H H OH H propan-1-01 propan-2-01 (l-propanol) (2-propanol ) C,H,OH H H H H H H H H I I I I I I I I H-C-C-C-C-O-H H-C-C-C-C-H I I I I I I I I H H H H H H OH H butan-1-01 butan-2-01 (or 1-butanol) (o r 2-butanol) C, H lI OH H H H H H H H H H H H H H H H I I I I I I I I I I I I I I I H-C-C-C-C-C-O- H H-C-C-C-C-C-H H-C-C -C-C-C-H I I I I I I I I I I I I I I I H H H H H HHHOH H H H OH H H pentan-1-01 pentan-2-01 pentan-3-01 (o r 1-pentanol) (o r 2-pentanol) (or 3-pentanol) Note The unbranched isomers of hexanol (C,H"OH) are drawn and named in the same way as those of pentanol. 14 Organic chemistry - an introduction Alkanoic acids: C n H 2n+, COOH or R-COOH Alkanoic acids (or carboxylic acids) have the carboxyl group (-COOH) as their functional group: /-0 -c '" "O-H Table 14.9 Names and formulae of the first six alkanoic acids HCOOH /-0 C,H,COOH H H H H-C/ I I I ~ O H-C-C-C-C " O- H methanoic acid H I I H H I "O-H butanoic acid CH,COOH H C,H,COOH H H H H I ~o I I I I ~o H-C-C H-C-C-C-C-C I I I I I H "O-H H H H H "O-H ethanoic acid pentanoic acid C,H5 COOH H H C5H I1 COOH H H H H H I I ~o I I I I I ~o H-C-C-C H- C-C-C-C-C - C I I I I I H H O- H " H I H H H H I "O-H propanoic acid hexanoic acid Revision questions 1 What are organic compound s? 2 a Why is carbon capable of forming a huge number of different organic compounds? b Show, by means of a dot and cross diagram, how the atoms are bonded in the ethane molecule. 3 What is EACH of the following: a a functional group b a fully displayed structural formula c a homologous series? 4 a Give FOUR characteristics of a homologous series. b Explain how straight chain members of a homologous series are named. 5 Give the general formula for members of EACH of the following homologous series: a alcohol series b alkene series c alkanoic acid series d alkane series 6 Give the name and fully displayed structural formula of EACH of the following straight chain molecules: a an alkene with THREE carbon atoms b an alcohol with ONE carbon atom c an alkane with FOUR carbon atoms d an alkanoic acid with TWO carbon atoms 14 Concise Revision Course: CSEC· Chemistry 7 Name the homologous series to which EACH of the following compounds belongs and name EACH compound: d C, H, 8 Define 'structural isomerism'. 9 Name the following compounds: H H H H H H H H H H H H I I I I I I I I / I I I H- C- C- C- C- H H-C-C- C- C=C H-C-C-C-H I I H H I H I I H H I I H "H I I H OH H I H- C- H I H A B c 10 Draw the structural formula of EACH of the follow ing: a hex-3-ene b 2-methylpropene C 2,3-dimethylbutane 14 Organic chemistry - an introduction 15 Sources of hydrocarbon compounds Hydrocarbons are organic compounds composed of carbon and hydrogen atoms only. Alkanes and alkenes are both hydrocarbons. Natural sources of hydrocarbons There are two natural sou rces of hydrocarbons: Natural gas Natural gas is a mixture of the first four alkanes, mainly methane (CH) with small amounts of ethane (C, H,), propane (C, H, ) and butane (C,H lO ). Before natural gas is sold comme rciall y, the propane and butane are removed, leaving a mixture of methane and ethane. The propane and butane are then liquefied under pressure to produce liquefied petroleum gas, also known as LPG or 'bottled gas'. Crude oil (or Petroleum) Crude oil is a yellow to black Oily liqu id found in the earth. It is a complex mixture consisting of a large number of different solid and gaseous hydrocarbons dissolved in liqu id hydrocarbons, mainly alkanes and some ringed compounds. To make it useful, petroleum is separated into its different components (or 'fractions') by fractional distillation at an oil refin ery. Fractional distillation of crude oil Any impurities are first removed from th e crude o il and then it is heated to about 400 °C. This produces a mixture of liqui d and vapour which is piped into the bottom part of a fractionating tower. The vapours rise up the tower and the viscous liquid fraction, known as bitumen or asphalt, sink s to the bottom of the tower and is tapped off. The vapours rising up the tower pass through a series of bubble caps and trays where they may condense. The temperature decreases going up the tower and the lower the boiling point of the hydrocarbon, the furth er the vapour will rise before condensing. The liquids produced when the vapours condense are tapped off at the different leve ls. Gases that do not condense are removed at the top of the tower as refinery gas. Each fraction tapped off is a mixture of hydrocarbons with similar sized molecules and boiling points. The different fractions have different uses. They are mainly used as fuels and lubricants, and to manufacture a variety of petrochemicals (see Figure 15.1, p. 135). Fractionating towers at an oil refinery 15 Concise Revision Course: CSEC· Chemistry  Fraction Uses ----... refinery gas Fuel for domestic use. e.g. cooking. To manufacture various petrochemicals. bubble - petrol (gasoline) Fuel for internal combustion engines, e.g. cars, light aircraft, boats. tray - naphtha To manufacture various petrochemicals. - ~ ~ ~ kerosene oil Fuel for jet engines, cooking, ~ ~ (paraffin oil) heating, lighting, e.g. ker.osene lamps.., -s v - 0 ',r. E a ~ 0; diesel oil Fu~ ! for diesel engines, ~ e.g. cars, trucks, buses, c trains, tractors, boats, generators. " 5 - 0 M "5 fuel oils Fuel for ships, factories, "' power stations, heating. - ~ ---+- lubricating oils Lubricants in machinery and waxes and vehicle engines. heated Used to make polishing petroleum - ~ -. waxes, petroleum jelly, candles. ,,_ _ _ _ _ _......... bitumen Surfacing roads, car parks, (asphalt) airport runways. Roofing. Figure 15.1 Uses of the frac tions produced by fractional distillation o f crude oil Cracking hydrocarbons Cracking is the process by which long chain hydrocarbon molecules are broken down into shorter chain hydrocarbon molecules by breaking carbon- carbon bonds. Crac king is important for two re ason s: Cracking increases th e production of the smaller, more useful hydrocarbons, su ch as petrol. Fractional distillation produces an exce ss of the larger hydrocarbon molecule s and in s ufficient of the s maller one s to meet current de mand s. 15 Sources of hydrocarbon compound s  Cracking prod uces th e very reacti ve alkenes which are used in the petrochemical industry to make many other useful organic co mpou nd s. Fraction al distillation does not produce alkenes, whereas cracki ng always resu lts in the formation of at least one alkene. Crack in g can be carried out in two ways: Thermal cracking, which uses temperatures up to about 750°C and press ures up to 70 atmospheres. Catalytic cracking, which uses temperatures of about 500 °c , at fairl y low pressures in the presence of a catalyst. H H H H H H H H H H H H I I I I I H-C - C-C - C- C-C- H I I I I I I I ~ I I I I I H-C-C- C-C- H I I I + "C= C"- / / H H H HHHHH H H H H C6H 14 ~ C4 HlO + hexane butane Figure 15.2 One possible way of cracking hexan e Revision questions 1 What are hyd rocarbo ns? 2 Ident ify TWO nat ural sources of hydroca rb o ns. 3 Outline the process by which crude oil is separated into different fractions. 4 Name FOUR fract io ns obtained when crude o il is fractionally distilled, and give ONE majo r use of EACH fraction named. 5 a What happen s when hydroca rbo ns are cracked? b Give TWO rea sons why cracking hyd ro ca rbon s is important. 6 Pentane (CsH12 ) can be cracked in THREE different ways to produ ce TWO different co mpo unds in EACH case. Show, by means of chemical equations, the THREE different ways pentan e can be cracked and name the product s in EACH case. 15 Concise Revision Course: CSEC· Chemistry 16 Reactions of carbon compounds The chemical reactions of carbon compounds are determin ed by the reactions of th e functional group (or groups) present in the compounds. Alkanes are saturated hydrocarbons, meaning th ey have on ly single bonds between adjacent carbon atoms. A lkanes with 1 to 4 carbo n atoms in their molecules are gases at room temperature, those w ith 5 to 16 ca rbon atoms are liquids and th ose with 17 or more carbo n atoms are solids. Alk anes are relatively unreactive because the carbon-ca rbo n sin gle bonds in th eir molecules are strong and not easi ly broken. Reactions of alkanes Alkanes burn easily in air or oxygen Alka nes burn in air or oxygen to form carbon dioxide and water as steam. They burn w ith clear, blue, non-smoky flames because they have a low ratio of carbon to hydrogen atoms in their molecules. All the carbo n is converted to carbon dioxide and no unreacted carbon remains in th e flames to make the m smoky. The reactions are exothermic, producing large amounts of heat energy. e.g. CH,(g) + 20,(g) --.... CO, (g) + 2H,O(g) t1 H -ve Alkanes undergo substitution reactions with halogens Unde r the correct conditions, alkanes undergo substitution reactions with halogens. In these reactions, the hydrogen atoms in the alkan e mo lecu les are rep laced by halogen atoms such as chlorine or bromine. Fo r the reaction to occur, energy in th e form of light is required; ultraviolet light works best. The products of the halogenati o n of alkanes are known as haloalkanes o r alkyl halides. Example The reaction between methane and chlorine In the dark, no reaction occurs. In bright light, a rapid reaction occurs. In dim light, a slow substitution reaction occurs in stages, where one hydroge n atom is rep laced by one chlorine ato m at a time: light CH,(g) + CI,(g) CH, CI(g) + HCI (g) mon ochlo rometh ane hydrogen chloride light CH, CI(g) + CI,(g) CH,CI,(I) + HCI (g) dichloromethane light CH,CI,( I) + CI,(g) CHCI, (I) + HCI (g) trichloromethane light CHCI, (I) + CI,(g) CCI,(I) + HCI (g) tetrach loromethane 16 Reactions of carbon compounds  The overall reaction: light CH,(g) + 4CI, (g) --+-. CCI, (I ) + 4HCI (g) Similar substitutions occur with bromine vapour or bromine solution and with other alkanes, th ough th e reaction s are slower. During the reaction between bromin e and any alkane, the colour of th e bromine slowly fades from red brown to colourless in th e presence of UV light. This indicates that th e bromin e is being used up in the substitution reaction. Alkenes are unsaturated hydrocarbons because they each contain one carbon-carbon double bond. The presence of this double bond as their functional group makes alken es more reactive than alkanes. Reactions of alkenes Alkenes burn easily in air or oxygen Alkenes burn in air or oxygen to form carbon dioxide and water as steam. They burn with smoky yellow flames becaus e they have a higher rat io of carbon to hydrogen atoms in the ir molecules than alkanes. Not all the carbon is converted to carbon dioxide and th e unreacted ca rbon remain s, giving the flames a yellow, smoky appearance. The reactions are exothermic. e.g. C, H,(g) + 30 , (g) --+-. 2CO,(g) + 2H, O(g) i'.H-ve Alkenes undergo addition reactions Alkenes undergo addition reactions with other small molecules in which the alkene and th e ot her molecule react to form one molecul e. One bond in the double bond is broken and the compound form ed is saturated (it has no double bonds). X and Yare added one bond in a covalent bond at either side of the the double in the small original double bond bond breaks molecule breaks /\ , c=c / I/ alkene , + xL small molecule - -C-C- X Y I I saturated product I I Figure 16.1 Summary of addition reactions of alkenes Table 16.1 Addition reactions of alkenes ,. Product H H H H I I Addition of 'c=c/ / H , H + H-H Ni ca talyst 5 atm, 150"(· H-C-C-H I I H H alkanes hydrogen ethene hydrogen ethane Ni catalyst 0' C2H4(g) + H,(gJ 5 atm. 150°C· C2H6(g) 16 Concise Revision Course: CSE~ Chemistry  Product H H Br Br Ad dit ion of halogens "c=c / + Br -Bf -)~ 1 1 H-C-C- H (chlorin e gas, brom in e vapo ur, H/ " H 1 1 H H ethene bromine l,2·dibromoethane or a so lu ti o n of haloa lkanes bromi ne in wa te r or C2H4(g) + Br~g)