Cambridge CIE IGCSE Chemistry Past Paper PDF

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Your notes Chemistry Chemical Change & Rate of Reaction Contents Physical & Chemical Changes Rates of Reaction Factors Collision Theo...

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Your notes Chemistry Chemical Change & Rate of Reaction Contents Physical & Chemical Changes Rates of Reaction Factors Collision Theory Explaining Rates Using Collision Theory Investigating The Rate of a Reaction Interpreting Data Page 1 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Physical & Chemical Changes Your notes Physical & chemical changes Physical changes Physical changes do not produce any new chemical substances These changes are often: Easy to reverse Relatively easy to separate Examples of physical changes include: Changing state, e.g. melting / solid → liquid Making a mixture from 2 or more substances Dissolving a solute in a solvent Chemical changes During chemical changes / reactions, new chemical substances are formed that have very different properties to the reactants Most chemical changes are difficult to reverse There may be signs that a new substance has formed, such as: Colour changes Temperature changes Effervescence (fizzing) Colour change One example of a reaction that shows a colour change is the metal displacement reaction of silver and copper Orange-brown copper metal is added to a colourless solution of silver nitrate As the reaction proceeds the copper displaces the silver from the solution This causes two colour changes: 1. The solid inside the beaker changes from orange-brown to silver Page 2 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 2. The solution changes from colourless to blue The metal displacement reaction of silver and copper Your notes The reaction shows two colour changes; one in the colour of the solution and one in the colour of the solid Another reaction, from the syllabus, that shows a clear colour change is the halide ion test From colourless to cream / white / yellow depending on the halide ion This also includes a change of state as a solid / precipitate is formed Temperature change Chemical reactions that give a temperature change can be grouped into two categories: Those that give out heat / thermal energy - exothermic Those that take in heat / thermal energy - endothermic Exothermic reactions Some examples of reactions that cause an increase in temperature are: The reaction of calcium oxide with water to form calcium hydroxide is highly exothermic The reaction of sodium with water is exothermic and effervesces Endothermic reactions Page 3 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Reactions that cause a decrease in temperature are less commonly talked about than exothermic reactions Your notes Examples include: Photosynthesis Light energy is absorbed during the process of converting carbon dioxide and water into glucose and oxygen When solid ammonium chloride is dissolved in water Heat / thermal energy is absorbed from the surroundings, causing the temperature to decrease This reaction is commonly used in cold packs Effervescence Effervescence, or fizzing, is another sign of a chemical reaction Chemical reactions that cause effervescence often involve acids: The reaction of alkali metals with water The reaction of the alkali metals, such as sodium, with water releases hydrogen gas Metal + water → metal hydroxide + hydrogen There are other signs of a chemical reaction including: A change of physical state, e.g. liquid → solid Light being produced A smell being produced A change in pH Page 4 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Rates of Reaction Factors Your notes Rates of reaction factors Factors that can affect the rate of a reaction are: The concentration of the reactants in solution or the pressure of reacting gases Surface area of solid reactants The temperature of the reaction The presence of a catalyst Changes in these factors directly influence the rate of a reaction It is of economic interest to have a higher rate of reaction as this implies a higher rate of production and hence a more efficient and sustainable process The effect of increased concentration or pressure Graph showing the effect of concentration on rate of reaction Page 5 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Increasing the concentration of a solution or gas pressure increases the rate of reaction Explanation: Compared to a reaction with a reactant at a low concentration (or pressure), the line graph for the same reaction at a higher concentration (or pressure): Has a steeper gradient at the start Becomes horizontal sooner Forms the same amount of product This shows that increasing the concentration (or pressure) increases the rate of reaction The effect of increasing surface area Graph showing the effect of surface area on rate of reaction Page 6 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Increasing the surface area increases the rate of reaction Explanation: Compared to a reaction with lumps of reactant, the line graph for the same reaction with powdered reactant: Has a steeper gradient at the start Becomes horizontal sooner Forms the same amount of product This shows that increasing the surface area increases the rate of reaction Increasing surface area can sometimes be described as decreasing solid particle size Surface area and particle size Page 7 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Surface area increases as particle size decreases. A 2 cm3 cube has a surface area of 24 cm2 and the same cube cut up into 8 cubes has a surface area of 48 cm2 The effect of increasing temperature Graph showing the effect of temperature on rate of reaction Increasing the temperature increases the rate of reaction Page 8 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Explanation: Compared to a reaction at a low temperature, the line graph for the same reaction at a higher Your notes temperature: Has a steeper gradient at the start Becomes horizontal sooner Forms the same amount of product This shows that increasing the temperature increases the rate of reaction The effect of using a catalyst Catalysts are substances which speed up the rate of a reaction without themselves being altered or consumed in the reaction The mass of a catalyst at the beginning and end of a reaction is the same and they do not form part of the equation Graph showing the effect of using a catalyst on rate of reaction Graph showing the effect of using a catalyst on the rate of reaction Explanation: Page 9 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Compared to a reaction without a catalyst, the graph line for the same reaction but with a catalyst has a steeper gradient at the start and becomes horizontal sooner Your notes This shows that with a catalyst, the rate of reaction will increase Page 10 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Collision Theory Your notes Collision theory Extended tier only What is collision theory? Collision theory states that in order for a reaction to occur: The particles must collide with each other The collision must have sufficient energy to cause a reaction i.e. enough energy to break bonds The minimum energy that colliding particles must have to react is known as the activation energy Collisions can be described as successful or unsuccessful A successful collision means that the reactant particles collide and rearrange to form the products This happens when the particles have sufficient energy (i.e. energy greater than the activation energy) to react The collision is successful resulting in a rearrangement of atoms to form the products An unsuccessful collision means that the reactant particles just bounce off each other and remain unchanged This happens when the particles do not have sufficient energy to break the necessary bonds or do not collide in the correct orientation Page 11 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The collision is unsuccessful resulting in no rearrangement of atoms How to increase the number of successful collisions Your notes Increasing the number of successful collisions means that a greater proportion of reactant particles collide to form product molecules The number of successful collisions depends on: The number of particles per unit volume - more particles in a given volume will produce more frequent successful collisions The frequency of collisions - a greater number of collisions per second will give a greater number of successful collisions per second The kinetic energy of the particles - greater kinetic energy means a greater proportion of collisions will have an energy that exceeds the activation energy and the more frequent the collisions will be as the particles are moving quicker, therefore, more collisions will be successful The activation energy - fewer collisions will have an energy that exceeds higher activation energy and fewer collisions will be successful These all have an impact on the rate of reaction which is dependent on the number of successful collisions per unit of time Page 12 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Explaining Rates Using Collision Theory Your notes Explaining rates using collision theory Extended tier only Collision theory can explain why concentration, pressure, surface area, temperature and catalysts affect the rate of a chemical reaction How increasing concentration affects rate Increasing the concentration of a solution increases the rate of reaction Increasing the concentration means that there are more reactant particles in a given volume This causes more collisions per second Leading to more frequent and successful collisions per second Therefore, the rate of reaction increases If you double the number of particles, you will double the number of collisions per second The number of collisions is proportional to the number of particles present Diagram showing the effect of increasing concentration A higher concentration of particles in (b) means that there are more particles present in the same volume than (a) so the number of collisions and successful collisions between particles increases causing an increased rate of reaction Page 13 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Examiner Tips and Tricks When answering questions on the effect of concentration on the rate of reaction, you should mention that there are more particles per unit volume (usually cm3) and this causes an increase in the rate of collisions. How increasing pressure affects rate Increasing the pressure of a gas increases the rate of reaction Increasing the pressure means that there are the same number of reactant particles in a smaller volume This causes more collisions per second Leading to more frequent and successful collisions per second Therefore, the rate of reaction increases Diagram showing the effect of increasing pressure The higher pressure (b) means that there are the same number of particles present in a smaller volume than (a) so the number of collisions and successful collisions between particles increases causing an increased rate of reaction How increasing the surface area affects rate Increasing the surface area increases the rate of reaction Page 14 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Increasing the surface area means that a greater surface area of particles will be exposed to the other reactant Your notes This causes more collisions per second Leading to more frequent and successful collisions per second Therefore, the rate of reaction increases If you double the surface area, you will double the number of collisions per second Diagram showing the effect of increasing surface area An increase in surface area means more collisions per second How increasing temperature affects rate Increasing the temperature increases the rate of reaction Increasing the temperature means that the particles have more kinetic energy This causes more collisions per second Leading to more frequent and successful collisions per second Therefore, the rate of reaction increases The effect of temperature on collisions is not so straightforward as concentration or surface area; a small increase in temperature causes a large increase in rate For aqueous and gaseous systems, a rough rule of thumb is that for every 10 oC increase in temperature, the rate of reaction approximately doubles Page 15 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Diagram showing the effect of increasing temperature Your notes An increase in temperature causes an increase in the kinetic energy of the particles. The number of successful collisions increases How a catalyst affects rate Catalysts are substances which speed up the rate of a reaction without themselves being altered or consumed in the reaction Different processes require different types of catalysts but they all work on the same principle A catalyst provides a different reaction pathway that has a lower activation energy This means a higher proportion of the reactant particles have energy greater than the activation energy and will result in more successful collisions per second Page 16 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A catalyst lowers the activation energy of a reaction by providing an alternative reaction pathway An important industrial example is iron, which is used to catalyse the Haber Process for the production of ammonia Iron beads are used to increase the surface area available for catalysis Enzymes are biological catalysts, they work best at specific temperature and pH ranges Normally only small amounts of catalysts are needed to have an effect on a reaction Examiner Tips and Tricks Temperature is the only factor that directly affects the energy of collisions because the increased thermal energy is converted to increased kinetic energy in the particles Concentration, pressure and surface area only affect the number of collisions Temperature affects reaction rate by increasing the number of collisions and increasing the energy of the collisions Of these two, the increase in energy is the more important one. Page 17 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Investigating The Rate of a Reaction Your notes Investigating the rate of a reaction To measure the rate of a reaction, we need to be able to measure: How quickly the reactants are used up OR How quickly the products are formed The method used for measuring depends on the substances involved There are a number of ways to measure a reaction rate in the lab They all depend on a property changing during the course of the reaction Properties that change during the course of a reaction include: Colour Mass Volume The changing property is taken to be proportional to the concentration of the reactant or product Faster reactions can be easier to measure when the reaction is over This can be done by averaging a collected measurement over the course of the reaction Some reaction rates can be measured as the reaction proceeds (this generates more data) Three commonly used techniques are: measuring mass loss on a balance measuring the volume of a gas produced measuring a reaction where there is a colour change at the end of the reaction Investigating the effect of concentration of a solution on the rate of reaction Page 18 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 19 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Diagram showing the apparatus needed to investigate the effect of concentration on the rate of reaction Method: Measure 50 cm3 of sodium thiosulfate solution into a flask Measure 5 cm3 of dilute hydrochloric acid into a measuring cylinder Draw a cross on a piece of paper and put it underneath the flask Add the acid into the flask and immediately start the stopwatch Look down at the cross from above and stop the stopwatch when the cross can no longer be seen Repeat using different concentrations of sodium thiosulfate solution (mix different volumes of sodium thiosulfate solution with water to dilute it) Result: With an increase in the concentration of a solution, the rate of reaction will increase This is because there will be more reactant particles in a given volume, allowing more frequent and successful collisions, increasing the rate of reaction Investigating the effect of surface area on the rate of reaction Page 20 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Diagram showing the process of downwards displacement to investigate the effect of the surface area of a solid on the rate of reaction Method: Add dilute hydrochloric acid into a conical flask Use a delivery tube to connect this flask to a measuring cylinder upside down in a bucket of water (downwards displacement) Add magnesium ribbon to the conical flask and quickly put the bung back into the flask Measure the volume of gas produced in a fixed time using the measuring cylinder Repeat with different size pieces of magnesium ribbon The same total mass of magnesium must be used Result: Smaller pieces of magnesium ribbon cause an increase in the surface area of the solid, so the rate of reaction will increase This is because more surface area of the particles will be exposed to the other reactant so there will be more frequent and successful collisions, increasing the rate of reaction Investigating the effect of temperature on the rate of reaction Page 21 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 22 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Diagram showing the apparatus needed to investigate the effect of temperature on the rate of reaction Method: Dilute hydrochloric acid is heated to a set temperature using a water bath Add the dilute hydrochloric acid into a conical flask Add a strip of magnesium and start the stopwatch Stop the time when the magnesium fully reacts and disappears Repeat at different temperatures and compare results Result: With an increase in the temperature, the rate of reaction will increase This is because the particles will have more kinetic energy than the required activation energy, therefore more frequent and successful collisions will occur, increasing the rate of reaction Investigating the effect of a catalyst on the rate of reaction Page 23 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 24 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Diagram showing the apparatus needed to investigate the effect of a catalyst on the rate of reaction Method: Your notes Add hydrogen peroxide into a conical flask Use a delivery tube to connect this flask to a measuring cylinder upside down in a tub of water (downwards displacement) Add the catalyst manganese(IV) oxide into the conical flask and quickly place the bung into the flask Measure the volume of gas produced in a fixed time using the measuring cylinder Repeat experiment without the catalyst of manganese(IV) oxide and compare results Result: Using a catalyst will increase the rate of reaction The catalyst will provide an alternative pathway requiring lower activation energy so more colliding particles will have the necessary activation energy to react This will allow more frequent and successful collisions, increasing the rate of reaction Monitoring changes in mass Many reactions involve the production of a gas which will be released during the reaction The gas can be collected and the volume of gas monitored as per some methods above Alternatively, the reaction can be performed in an open flask on a balance to measure the loss in mass of reactant Cotton wool is usually placed in the mouth of the flask which allows gas out but prevents any materials from being ejected from the flask (if the reaction is vigorous) Page 25 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Diagram showing the set-up for measuring the rate of reaction by loss in mass This method is not suitable for hydrogen and other gases with a small relative formula mass, Mr as the loss in mass may be too small to measure Examiner Tips and Tricks There are many different methods of investigating the rate of reaction. Another method of gas collection you may see uses a gas syringe. Extended tier students may be required to devise and evaluate methods of investigating rates of reaction. Evaluating investigations of rates of reactions Extended tier only Page 26 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources When investigating rates of reaction, there are a number of different methods that can be used to carry out the same investigation Your notes Evaluating what is the best method to use is part of good experimental planning and design This means appreciating some of the advantages and disadvantages of the methods available Advantages and disadvantages of methods of investigating rates of reaction Experiment Advantage Disadvantage Formation of a solid / Simple experiment Difficult to determine when the cross is obscured precipitate with no specialist as people will determine the cross to have equipment disappeared at different levels of cloudiness (Disappearing cross experiment) Easy to contaminate equipment Gas collection using a Works for all reactions Gas syringes are fragile and expensive gas syringe that produce a gas Gas syringes can stick All the gas collected is from the reaction They can collect limited volumes Easy to set up Gas is lost while the bung is connected to the reaction flask Gas collection using an Works for all reactions The delivery tube can pop out of the measuring inverted measuring that produce a gas cylinder cylinder Uses common lab It can be difficult to read the scale as it is upside equipment down and may be obscured by bubbles Gas is lost while the bung is connected to the reaction flask Measuring mass lost on a Easy to set up Not suitable for gases with low molecular mass balance Uses common lab equipment Page 27 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Interpreting Data Your notes Interpreting data Data recorded in rate studies is used to plot graphs to calculate the rate of a reaction Plotting a graph until the completion of the reaction shows how the rate of reaction changes with time The rate of reaction is always quickest at the start of the chemical reaction This is when there are the most reactants available to collide and form products On a graph, the line at the start of the reaction has the steepest gradient As the reaction progresses, the rate of reaction decreases This is because the concentration of reactants decreases as they are being used up On a graph, the line becomes less steep The reaction eventually stops This is because at least one of the reactants has been used up The rate of reaction is now zero On a graph, this is when the line becomes horizontal The amount of product formed in a reaction is determined by the limiting reactant: If the amount of limiting reactant increases, the amount of product formed increases If the amount of the reactant in excess increases, the amount of product remains the same You can plot more than one run of a variable on the same graph making it easier to see how the variable influences the rate For example, plotting the effect of concentration on a reaction between the acid and marble chips Page 28 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Drawing a tangent to the slope allows you to show the gradient at any point on the curve A steeper slope means a quicker reaction and a higher rate of reaction The volume of a gaseous product would increase to a maximum over time So, the line levels out indicating the reaction is over Since the volume and mass would be proportional, this could also be a graph of the mass of product versus time Worked Example Page 29 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 0.2 g of manganese(IV) oxide was added to 25 cm3 of 0.1 mol / dm3 hydrogen peroxide solution. The volume of oxygen produced every minute was recorded and the results are shown on the graph. Your notes The experiment was repeated using the same mass of manganese(IV) oxide and at the same temperature but using 25 cm3 of 0.2 mol / dm3 of hydrogen peroxide solution. Sketch the curve for the results of this experiment on the same grid. Answer: 1. Deduce how the initial gradient will be different from the original graph The hydrogen peroxide solution is twice as concentrated So, the rate of reaction will be greater and the initial gradient will be steeper 2. Deduce how much product will be formed compared to the original experiment The amount of hydrogen peroxide determines the amount of oxygen produced Page 30 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources In the 2nd experiment, there are twice as many hydrogen peroxide molecules in the same volume So, this will produce double the amount of oxygen in the same time Your notes 3. Sketch the graph Calculating the rate of reaction at a particular point To calculate the rate of reaction at any given time / point in a chemical reaction, you need to find the gradient of the curve at that time / point To do this: Draw a tangent to the curve Calculate the change in the y-axis Calculate the change in the x-axis Calculate the gradient of the tangent using: Page 31 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources change in y Rate of reaction (or gradient) = change in x Your notes Worked Example Iodine and methanoic acid react in aqueous solution. I2 (aq) + HCOOH (aq) → 2I− (aq) + 2H+ (aq) + CO2 (g) The rate of reaction can be found by measuring the volume of carbon dioxide produced per unit time and plotting a graph as shown: Calculate the rate of reaction at 20 seconds. Answer: Draw a tangent to the curve at 20 seconds: Page 32 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Complete the triangle and read off the values of x and y Determine the rate of reaction / gradient of the line: change in y Rate of reaction (or gradient) = change in x 24 Rate of reaction (or gradient) = = 0.60 cm3 / s 40 Examiner Tips and Tricks If the amount of reactant used up is being monitored, then the graph will fall with the steepest gradient at the start, becoming less steep until it levels off to a horizontal line. Page 33 of 33 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers