Chemical Reaction PDF

1-Rate of reaction 2-Redox Reactionss 3-Reversible Reaction Rate of Reaction [**2.1 **[2 ways to measure speed of reaction]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-2-ways-to-measure-speed-of-reaction) [**2.1.1 **[1. Measuring time for reaction to complete]](http:...

1-Rate of reaction 2-Redox Reactionss 3-Reversible Reaction Rate of Reaction [**2.1 **[2 ways to measure speed of reaction]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-2-ways-to-measure-speed-of-reaction) [**2.1.1 **[1. Measuring time for reaction to complete]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-1.-Measuring-time-for-reaction-to-complete) [**2.1.2 **[2. Measuring the amount of product produced in a period of time or measuring the amount of reactant remain in a period of time.]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-2.-Measuring-the-amount-of-product-produced-in-a-period-of-time-or-measuring-the-amount-of-reactant-remain-in-a-period-of-time.) [**2.2 **[Factors Affecting Speed of Reaction]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Factors-Affecting-Speed-of-Reaction) [**2.2.1 **[1. Particle Size of Reactant]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-1.-Particle-Size-of-Reactant) [**2.2.2 **[2. Concentration of Reactant]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-2.-Concentration-of-Reactant) [**2.2.3 **[3. Pressure of Reactant]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-3.-Pressure-of-Reactant) [**2.2.4 **[4. Temperature of Reaction]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-4.-Temperature-of-Reaction) [**2.2.5 **[5. Effect of Catalyst]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-5.-Effect-of-Catalyst) [**2.2.6 **[Enzymes]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Enzymes) [**2.3 **[Exothermic Reaction]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Exothermic-Reaction) [**2.3.1 **[Examples of exothermic changes]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Examples-of-exothermic-changes) [**2.4 **[Endothermic Reaction]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Endothermic-Reaction) [**2.4.1 **[Examples of endothermic changes:]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Examples-of-endothermic-changes:) [**2.5 **[Endothermic vs Exothermic Reactions]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Endothermic-vs-Exothermic-Reactions) [**2.6 **[Heat of Reaction]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Heat-of-Reaction) [**2.6.1 **[Exothermic reaction:]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Exothermic-reaction:) [**2.6.2 **[Endothermic reaction:]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Endothermic-reaction:) [**2.7 **[Heat Energy and Enthalpy Change in Reaction]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Heat-Energy-and-Enthalpy-Change-in-Reaction) [**2.7.1 **[Worked Example]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Worked-Example) [**2.8 **[Activation energy]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Activation-energy) [**2.9 **[Exothermic and Endothermic Reaction Graph]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Exothermic-and-Endothermic-Reaction-Graph) [**2.10 **[Fuels]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Fuels) [**2.10.1 **[Fuel Cells]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Fuel-Cells) [**2.11 **[Petroleum]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Petroleum) [**2.12 **[Photosynthesis]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Photosynthesis) [**3 **[MCQ Questions]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-MCQ-Questions) [**3.1 **[MCQ Answers]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-MCQ-Answers) [**4 **[Worked Solutions]](http://www.gcestudybuddy.com/chemistry-classroom/rate-of-reactions#TOC-Worked-Solutions) +-----------------------------------------------------------------------+ | **ways to measure speed of reaction** | | | | ***1. Measuring time for reaction to complete*** | | | | - Speed of reaction is inversely proportional to time taken; the | | shorter the time needed for reaction to complete, the faster the | | speed of reaction is. | | | | Speed of reaction =1/time taken\ | | Speed of reaction A = = 0.333/s\ | | Speed of reaction B = = 0.667/s\ | | \ | | Therefore reaction B is faster than reaction A as time taken for B is | | shorter\ | | Number of times B faster than A = = 2 times | | | | ***2. Measuring the amount of product produced in a period of time or | | measuring the amount of reactant remain in a period of time.*** | | | | - Can be measured by plotting change in volume of gas evolved, mass | | of reaction mixture as reaction proceeds and change of pressure | | of gas formed. | | | | **A. Measuring the amount of gas evolved.** | | | | - Consider reaction of limestone with acid to produce carbon | | dioxide. | | | | - A syringe is used to help in measurement of gas produced in | | volume every time interval. | | | | - A graph of volume of gas against time is plotted. | | | | - Gradient largest at start indicating speed at its greatest. | | | | - Gradient decreases with time -- speed decreases with time. | | | | - Gradient becomes zero, speed is zero. The reaction has | | finished. | | | | http://www.gcestudybuddy.com/\_/rsrc/1378817358305/chemistry-classroo | | m/rate-of-reactions/gas\_collection2.gif?height=212&width=320 | | | | **\ | | B. Measuring change in mass of reaction mixture.** | | | |  | | | | - Marble is reacted with acid in a flask with cotton wool stucked | | at top to prevent splashing during reaction but it allows gas to | | be free. | | | | - The reading on balance is plotted on a graph on every time | | interval. | | | | Factors Affecting Speed of Reaction | | | | ***1. Particle Size of Reactant*** | | | | **Increase in particle size, Rate of reaction will decrease** | | | | **Reason**: For the same mass of particles (e.g. 1kg) the smaller the | | particles are the faster the reaction will take place. This is | | because many small particles will have more surface area than fewer | | large particles. More surface area means that there is more area in | | which particles can collide. More collisions per unit of time means a | | faster reaction. | | | | - When large marble is reacted with acid and compared to reaction | | of fine marble solids being reacted with acid and the graph of | | volume of gas against time is plotted, it is found that the | | reaction involving finer marble chips produces gas faster than | | the one with larger marble chunk as the graph of finer chips is | | steeper. | | | | - The volume of gas at the end is the same for both reactions. | | | | - Therefore, reactions of solids with liquid/gas is faster when the | | solids are of smaller pieces | | | | - Reactions occur when particles collide.  | | | | - Small particles creates larger surface area for more collisions | | between reacting particles which increases speed of reaction. | | | | - Explosions: chemical reactions occuring extremely rapid rate | | producing heat+gas | | | | - **Examples** | | | | - Coal dust burn faster than large pieces as it has larger | | surface area. In coal mines, when air contains too much coal | | dust, explosion can occur from a single spark or match. Water | | is sprayed into the air to remove coal dust. | | | | - Flour in mills can ignite easily due to large surface area. | | | | ***2. Concentration of Reactant*** | | | | - **Increase in the concentration of a solution, the rate of | | reaction will increase** | | | | | | | | - **REASON** | | | | - This is because there will be more reactant particles in a given | | volume, allowing more frequent and successful collisions per | | second, increasing the rate of reaction. | | | | ***3. Pressure of Reactant*** | | | | - Only gaseous reactions are affected as gas is compressible. | | | | - At higher pressure, molecules are forced to move closely | | together, hence increasing the particles per unit volume of gas | | and effectively increases the collision between reacting | | molecules so the speed of reaction increases. | | | | - High pressure is used in industrial processes (e.g. Haber Process | | Plant) so that the reaction goes faster. | | | | ***4. Temperature of Reaction*** | | | | - Speed of reaction increases when temperature increases. | | | | - Particles don't always react upon collision but just bounce as | | they don't have enough activation energy to react. | | | | - With increase in temperature, particles absorb the energy and | | having enough activation energy, they move faster and collide | | more effectively per second. | | | | - Therefore, speed of reaction is increased. | | | | - Usually, speed of reaction doubles for every 10oC rise in | | temperature. | | | | ***5. Effect of Catalyst*** | | | | - Catalysts are chemical substances which alters speed of reaction | | without itself being used at the end of a reaction. | | | | - It can be reused and only small amount of catalyst is needed to | | affect a reaction. | | | | - transition metals (e.g. Titanium, Nickel, Iron, Copper) are good | | catalysts | | | | - most catalyst catalyse one kind of reaction (except titanium) | | | | - Catalysts lower the need of energy to break bonds so activation | | energy is lower. | | | | - Consequently, bond breaking occurs easily and more often when | | particles collide | | | | http://www.gcestudybuddy.com/\_/rsrc/1309679805050/chemistry-classroo | | m/rate-of-reactions/Screen%20shot%202011-07-03%20at%20PM%2003.56.32.p | | ng | | | | **Factors Affecting Speed of Catalysed Reactions:**\ | | \ | | Speed of catalysed reactions can be increased by: | | | | - increasing temperature | | | | - increasing concentration of solutions | | | | - increasing pressure of gas reactions | | | | Catalyst provide "alternative path" which results in lower activation | | energy. | | | |  | | | | ***Enzymes*** | | | | Enzymes are biological catalysts\ | | \ | | **Characteristics of enzymes:** | | | | - They are very specific. One enzyme catalyse one type of reaction. | | | | - Sensitive to temperature. They work best at 40^o^C. Too high or | | too low temperatures destroy enzymes. | | | | - Sensitive to pH. They function within narrow range of pH. | | | | **Industrial uses of enzymes:** | | | | - They are added to detergents from bacteria, and also to make | | tough meat tender. These enzymes can be found in papaya fruit. | | | | - Yeast convert sugars into alcohol and carbon dioxide by | | fermentation. Beer, wine and soy sauce are made this way. | | | | - Fungal enzymes can be used to make antibiotics such as | | penicillin. | | | | **ENERGY FROM CHEMICALS** | | | | Exothermic Reaction | | | | - If more energy is released than is absorbed, then the reaction | | is **exothermic** | | | | - More energy is released when new bonds are formed than energy | | required to break the bonds in the reactants | | | | - The change in energy is negative since the products have less | | energy than the reactants | | | | - Therefore an exothermic reaction has a **negative** ΔH value | | | | | | | | - Exothermic change is one which heat energy is given out.  | | | | - Reaction is written as: | | | | - Reactants → Products + heat (or)  | | | | ***Examples of exothermic changes*** | | | | **1. Changes of State** | | | | - When gas condenses to water or water freezes to solid, heat is | | given out. | | | | - Eg. Condensation of steam to water | | | | - H~2~O (g) → H~2~O (l) + heat | | | | **2. Combustion reactions** | | | | - All combustion (burning) reactions are exothermic. | | | | - Eg. Burning of hydrogen in air | | | | - 2H~2 ~(g) + O~2 ~(g) → 2H~2~O (l) + heat | | | | **3. Dissolving of anhydrous salts/acids in water** | | | | - Dissolving solid salt to aqueous solution of the salt gives out | | heat | | | | - Eg. Dissolving of Na~2~CO~3~ in water (or CuSO~4~) | | | | - Na~2~CO~3 ~(s) → Na~2~CO~3~ (l) + heat | | | | | | | | - Eg. Dissolving of concentrated acid in water | | | | - HCl (aq) + H~2~O (l) → less concentrated HCl (aq) + heat | | | | **4. Neutralization** | | | | - When acid and alkali react it gives out heat due to combining of | | H^+^ ions from acid and OH- ions from alkali to form water | | | | - H^+^ (aq) + OH^-^ (aq) → H~2~O (l) + heat | | | | **5. Metal Displacement** | | | | - Magnesium reacting with copper(II) sulphate | | | | - Mg (s) + Cu^2+ ^(aq) → Mg^2+ ^(s) + Cu (s) + heat | | | | Endothermic Reaction | | | | - If more energy is absorbed than is released, this reaction | | is** endothermic** | | | | - More energy is required to break the bonds than that gained from | | making the new bonds | | | | - The change in energy is positive since the products have more | | energy than the reactants | | | | - The symbol ΔH (delta H) is used to show the change in heat | | energy. H is the symbol for enthalpy, which is a measure of the | | total **heat** **of reaction** of a chemical reaction | | | | - Therefore an endothermic reaction has a **positive** ΔH value. | | | | | | | | - Reaction is written as: | | | | - Reactants + heat → Products (or) | | | | - Reactants → Products \[ΔH = + n kJ\], where n is amount of | | heat energy absorbed | | | | Endothermic Reaction ( Read ) \| Chemistry \| CK-12 Foundation | | | | ***Examples of endothermic changes:*** | | | | **1. Changes of states** | | | | - When solid melts to water & boils to steam, heat is absorbed to | | break the bond. | | | | - Eg. Condensation of steam to water | | | | - H~2~O (s) + heat → H~2~O (l) | | | | **2. Photolysis** | | | | - Reaction of light sensitive silver chloride in camera reel in | | light | | | | - 2AgBr (s) + heat → 2Ag (s) + Br~2~ (g) | | | | **3. Dissolving of Ionic Compounds** | | | | - Ionic compounds such as NH~4~Cl, KNO~3~, CaCO~3~ absorb heat from | | surroundings. | | | | - Eg. NH~4~Cl (s) + heat → NH~4~Cl (aq) | | | | - Eg. CuSO~4 ~(s) + heat → CuSO~4~ (aq) | | | | **4. Photosynthesis** | | | | - Light energy is absorbed by plants to produce starch. | | | | **5. Decomposition by heat** | | | | - Many compounds require heat for decomposition, e.g. CaCO~3~ to | | CO~2~ + CaO | | | | - CaCO~3 ~(s) + heat → CO~2~ (g) + CaO (s) | | | | **6. Acid + Bicarbonates (HCO3)** | | | | - NaHCO~3~ (s) + H~2~SO~4~ (aq) + heat → NaSO~4 ~(aq) + CO~2~ (g) + | | H~2~O (l) | | | | Endothermic vs Exothermic Reactions | | | | ------------------------------------------------------------------- | | --------------------------------------------------------------------- | | --------------------------------------- | | ** Exothermic Reactions    ** | | **Endothermic Reactions ** | | ------------------------------------------------------------------- | | -------------- ------------------------------------------------------ | | --------------------------------------- | | **1. Combustion** \ | | **1. Thermal decomposition** - using heat to break dow | | n larger molecules into smaller ones\ | | eg. methane + oxygen \--\> Carbon dioxide + steam + energy\ | | eg. calcium carbonate \-\-\--\> calcium oxide + carbon | | dioxide\ | | CH~4~ (g) + 2O~2~ (g) \-\--\> CO~2~ (g) + 2H~2~O (l) + energy | | CaCO3 (s) \-\--\> CaO (s) + CO2 (g)\ | | | | \ | | | | lead(II) nitrate \-\--\> lead(II) oxide + nitrogen dio | | xide + oxygen\ | | | | 2Pb(NO3)2 (s) \-\--\> 2PbO (s) + 4NO2 (g) + O2 (g)\ | | | | \ | | | | Copper(II) hydroxide \-\--\> Copper(II) oxide + water\ | | | | Cu(OH)2 (s) \-\--\> CuO (s) + H2O (l) | | | | **2. Respiration**\ | |   | | eg glucose + oxygen \--\> carbon dioxide + water + energy\ | | | | C6H12O6 (s) + 6O2 (g) \-\--\> 6CO2 (g) + energy | | | | | | **3. Neutralisation of acids and alkalis**\ | |   | | eg sodium hydroxide + hydrochloric acid \--\> sodium chloride + wat | | er + energy\ | | NaOH (aq) + HCl (aq) \-\--\> NaCl (aq) + H2O (l) + energy | | | | ------------------------------------------------------------------- | | --------------------------------------------------------------------- | | --------------------------------------- | | | | Heat of Reaction | | | | - The amount of energy given out or absorbed during a chemical | | reaction is enthalpy change.  | | | | - The symbol is ΔH measured in kilojoules (kJ). | | | | ***Exothermic reaction:*** | | | | - Mg (s) + CuSO~4 ~(aq) → MgSO~4~ (aq) + Cu (s) \[ΔH = --378 kJ\] | | | | - 378 kJ of heat energy is given out when 1 mol of Mg react with 1 | | mol CuSO~4~ to produce 1 mol of MgSO~4~ and 1 mol of Cu. | | | | ***Endothermic reaction:*** | | | | - CaCO~3 ~(s) → CO~2~ (g) + CaO (s) \[ΔH = +222 kJ\] | | | | - 222 kJ of heat energy is absorbed when 1 mol of CaCO~3~ decompose | | to 1 mol of CO~2~ and 1 mol of CaO. | | | | Heat Energy and Enthalpy Change in Reaction | | | | - When bonds are formed, heat energy is given out, | | it's **exothermic **and ΔH is **negative** | | | | - When bonds broken, heat energy is absorbed, | | it's **endothermic **and ΔH is **positive** | | | | ***Worked Example*** | | | | Hydrogen bromide is made by reacting H~2~ gas with Br~2~ gas. | | Calculate the heat change of the reaction given the equation and bond | | energy table below.\ | | \ | | H~2~ (g) + Br~2~ (g) → 2HBr (g) | | | | ** Covalent Bond** ** Bond energy (kJ/mol)** | | -------------------- --------------------------- | |  H -- H  436 | |  Br -- Br  224 | |  H -- Br  366 | | | | Bonds of H~2~ and Br~2~ molecules must be broken first to make HBr. \ | | Heat energy is absorbed to break these bonds by endothermic | | reaction.\ | | \ | | H -- H + Br -- Br → H H Br Br\ | | \ | | Broken bonds are used to make H -- Br bonds of HBr. Heat energy is | | released.\ | | \ | | H H Br Br → 2H -- Br\ | | \ | | Heat change can be calculated by: \ | | ΔH = heat released in making bonds + heat absorbed in breaking bonds\ | | **\ | | Exothermic ΔH **\ | | = the bond energy of 2 H -- Br bonds \ | | = 2(366) \ | | = -- 732 kJ\ | | \ | | **Endothermic ΔH **\ | | = the bond energy of 1 H -- H bond + 1 Br -- Br bond \ | | = 436 + 224 \ | | = + 660 kJ\ | | \ | | ΔH = -- 732 + 660 = -- 72 kJ\ | | \ | | Therefore more heat is given out in making bond than absorbed in | | breaking bond. \ | | The overall change is to give out heat and it's exothermic with ΔH | | negative. | | | | Activation energy | | | | - Activation energy is the minimum energy needed to start a | | reaction. | | | | - It is the energy needed to break the reactant bonds before new | | bonds are formed. | | | | - Reactions occur because of collision of particles and sufficient | | kinetic energy is needed to provide activation energy to break | | the bonds and start the reaction by providing extra energy from a | | heat source. | | | | Exothermic and Endothermic Reaction Graph | | | | - In exothermic reaction, enough energy given out in the reaction | | of particles to provide activation energy therefore less energy | | is needed to form products. | | | | - In endothermic reaction, insufficient energy is given out when | | bonds are made to provide activation energy for reaction to | | continue.  | | | | - More energy is needed to form products and heat must be | | continually added to fulfill energy requirement. | | | | Fuels | | | | - The combustion of fuels gives out large amount of energy in | | industries, transport & homes.  | | | | - These fuel mainly methane from coal, wood, oil, natural gas & | | hydrogen. | | | | -  Combustion in air provides energy and gives out heat. Hence, | | exothermic reaction. | | | | **Hydrogen as a Fuel** | | | | - Hydrogen provides twice as much as heat energy per gram than any | | other fuel and burns cleanly in air to form steam.  | | | | - They are mainly used as rocket fuel. | | | | **Production of Hydrogen** | | | | - Hydrogen is produced either by electrolysis of water or by | | cracking of hydrocarbon | | | | ***By cracking of hydrocarbon:*** | | | | - First, methane (hydrocarbon) and steam are passed over a nickel | | catalyst to form hydrogen and carbon monoxide. | | | | - CH~4 ~(g) + H~2~O (g) \--\> CO (g) + 3H~2~ (g) | | | | | | | | - The by-product carbon monoxide is not wasted. It is reacted with | | more steam to form carbon dioxide and hydrogen. | | | | - CO (g) + H~2~O (g) \--\> CO~2 ~(g) + H~2 ~(g) | | | | - Now you get more hydrogen. | | | | **By electrolysis:** | | | | - Water is electrolysed according to equation: | | | | - 2H~2~O (l) \--\> 2H~2~ (g) + O~2~ (g) | | | | - However, electrolysis is costly. | | | | **Creation of the Fuel**\ | | \ | | *In Engines:* | | | | - The hydrogen created is reacted with oxygen to form steam and | | heat energy | | | | - 2H~2~ (g) + O~2 ~(g) \--\> H~2~O (g) + heat | | | | This heat is needed to thrust the vehicle forward. However, we don't | | use heat energy for our daily appliances.  | | | | - Instead we use electrical energy and to make electrical energy | | from hydrogen, we use fuel cell | | | | ***Fuel Cells*** | | | | - A fuel cell converts chemical energy directly into electrical | | energy. | | | |  | | | | - Hydrogen reacts with hydroxide ions into electrolyte on the | | platinum catalyst on electrode to make the electrode | | negatively-charged. | | | | - H~2~ + 2OH^-^ \--\> 2H~2~O + 2e^-^ | | | | | | | | - Electrons flows past the load and to the other electrode. That | | negatively-charged electrode is now anode. Hydroxide ions | | constantly deposit electrons here to make water. While then, the | | other electrode is now cathode. | | | | - Oxygen reacts with water created on from hydrogen on the cathode | | to gain electrons from it: | | | | - O~2~ + 2H~2~O + 4e^- ^\--\> 4OH^-^ | | | | - If we combine the ionic equations, we still get water as product | | of hydrogen and oxygen, but the energy produced is now electrical | | energy: | | | | - 2H~2~ (g) + O~2~ (g) \--\> H~2~O (g) + electrical energy | | | |    **Advantages** | |  **Disadvantages** | | ---- -------------------------------------------------------------- | | ------------------------------------------ -------------------------- | | ------------------------------------------------ | |  1 Electrical energy can be generated continuously if there's con | | tinuous fuel supply Hydrogen-oxygen fuel cells | | are very expensive, hence limiting their use. | |  2 The by-product of fuel cells is steam, which do not pollute th | | e environment  Explosive | |  3  Chemical energy is efficiently converted to electrical energy | |. Hence there is minimal loss of energy.  Need more storage | | | | Petroleum | | | | - Petroleum is a mixture of hydrocarbons, which are compounds made | | up of carbon and hydrogen only. | | | | - Crude oil, freshly extracted from underground, undergo refining | | -- a process where oil undergoes fractional distillation to be | | separated into its fractions. | | | | - First, crude oil is heated up to 350oC and the vapours rise up a | | tower, divided with trays on some certain heights for the | | fractions to be collected.  | | | | - The fractionating column is cooler on top, hence upper trays | | collects fractions of low boiling points while the lower ones, | | being hotter, collect those with higher boiling points. | | | | Photosynthesis | | | | - Plants take in carbon dioxide and water in presence of | | chlorophyll and synthesize them in the presence of sunlight to | | produce glucose and release oxygen: | | | | - - **6CO~2~ + 6H~2~O \--\> C~6~H~12~O~6~ + 6O~2~** | | | | | | | | - Plants get their energy by using the glucose formed. Scientists | | believe that we can use the stored energy in glucose as | | combustible fuels. | | | | - First, glucose fermented to make ethanol by microorganisms such | | as yeast. This is fermentation. The glucose is usually derived | | from corn plant or sugar cane. | | | | - - **C~6~H~12~O~6~ → 2C~2~H~6~O + 2CO~2~** | | | | - Then, water is removed from ethanol by fractional distillation by | | heating it up until 78^o^C (boiling point of ethanol).  | | | | - Some water might still be present as the boiling point is close | | to ethanol. The ethanol produced is then mixed with fuel to be | | combusted to produce energy. This is biofuel, and it's a | | renewable energy source. | | | | *MCQ Questions* | | | | **1. If a strip of magnesium is dropped into excess hydrochloric acid | | an exothermic reaction occurs. The rate of reaction increases during | | the first few seconds because**\ | | a. the amount of magnesium is decreasing\ | | b. the magnesium is acting as a catalyst\ | | c. the solution is becoming hotter\ | | d. the surface area of the magnesium is increasing\ | | \ | | **2. The energy profile diagram show how adding a substance  to a | | reaction mixture changes the reaction pathway.** | | | | http://www.gcestudybuddy.com/\_/rsrc/1307461520719/chemistry-classroo | | m/rate-of-reactions/Screen%20shot%202011-06-07%20at%20PM%2011.45.07.p | | ng?height=194&width=320 | | | | **Which change is likely to be observed when X is added to the | | reaction mixture?**\ | | a. the reaction becomes less exothermic\ | | b. the reaction becomes more exothermic\ | | c. the speed of the reaction decreases\ | | d. the speed of the reaction increases\ | | \ | | **3. Dilute sulphuric acid reacts with copper(II) oxide to form | | copper(II) sulphate and water. What would not alter the rate of this | | reaction?**\ | | a. the concentration of the sulphuric acid\ | | b. the pressure at which the reaction takes place\ | | c. the size of the particles of copper(II) oxide\ | | d. the temperature of the reacting mixture\ | | \ | | **4. Zinc reacts with an excess of dilute sulphuric acid. The graph | | shows how the volume of hydrogen gas given off changed with time.** | | | |  | | | | **Why does the graph become horizontal at X?**\ | | a. all the sulphuric acid has reacted\ | | b. all the zinc has reacted\ | | c. hydrogen is being produced at a constant rate\ | | d. the reaction is beginning to slow down\ | | \ | | **5. Why is the reaction H~2~ + Cl~2~ \--\> 2HCl exothermic?**\ | | a. energy involved in the bonds breaking is greater than that of the | | bonds forming\ | | b. energy involved in the bonds forming is greater than that of the | | bonds breaking\ | | c. more bonds are broken than are formed\ | | d. more bonds are formed than are broken\ | | \ | | **6. Which of the following is an endothermic process?**\ | | a. the addition of water to anhydrous copper(II) sulphate\ | | b. the combustion of ethanol in air\ | | c. the formation of a carbohydrate and oxygen from carbon dioxide and | | water\ | | d. the oxidation of carbon to carbon dioxide\ | | **\ | | 7. Which process is exothermic?**\ | | a. burning petrol in a car engine\ | | b. cracking of oil fractions\ | | c. fractional distillation of oil\ | | d. melting bitumen for roads\ | | \ | | **8. Curve I is obtained by observing the decomposition of | | 100cm^3^ of 1mol/dm^3^ aqueous hydrogen peroxide, catalysed by | | manganese(IV) oxide.\ | | 2H~2~O~2~ (aq) \--\> 2H~2~O (l) + O~2~ (g)** | | | | http://www.gcestudybuddy.com/\_/rsrc/1307462231247/chemistry-classroo | | m/rate-of-reactions/Screen%20shot%202011-06-07%20at%20PM%2011.56.59.p | | ng?height=219&width=320 | | | | **Which alteration to the conditions will produce curve II?**\ | | a. adding some 0.1 mol/dm^3^ aqueous hydrogen peroxide\ | | b. lowering the temperature\ | | c. using a better catalyst\ | | d. using less manganese(IV) oxide\ | | \ | | **9. Why is Vanadium(IV) oxide used in the oxidation of sulphur | | dioxide to sulphur trioxide?**\ | | a. it acts as a reducing agent\ | | b. it prevents the decomposition of sulphur trioxide\ | | c. it removes impurities\ | | d. it speeds up the reaction\ | | **\ | | 10. Nitrogen and hydrogen react in a closed vessel.\ | | N~2~ (g) + 3H~2~ (g) \ 2NH~3~ (g)\ | | \ | | How do the speeds of the forward and reverse reactions change, if the | | pressure in the vessel is increased but the temperature is kept | | constant?** | | | |   ** speed of forward reaction** **speed of backward reaction* | | * | | ---- -------------------------------- ----------------------------- | | --- | |  a  increases increases | |  b  does not change  does not change | |  c  decreases  increases | |  d  decreases  does not change | | | | **\ | | 11. In the graph, curve X represents the results of the reaction | | between 1.0 g of granulated zinc and an excess of acid at 30^o^C.** | | | |  | | | | **Which changes will produce curve Y?**\ | | a. using 1.0 g of powdered zinc at 20^o^C\ | | b. using 1.0 g of granulated zinc at 20^o^C\ | | c. using 0.5 g of granulated zinc at 40^o^C\ | | d. using 0.5 g of granulated zinc at 20^o^C\ | | \ | | **12. Ethanol is produced by the fermentation of sugar. During the | | reaction, carbon dioxide is given off. The graph shows how the volume | | of carbon dioxide produced per minute varies with temperature.** | | | | http://www.gcestudybuddy.com/\_/rsrc/1307463121591/chemistry-classroo | | m/rate-of-reactions/Screen%20shot%202011-06-08%20at%20AM%2012.11.51.p | | ng?height=211&width=320 | | | | **Using the graph, decide which statement is correct?**\ | | a. the rate of reaction always increases with temperature\ | | b. the rate of reaction reaches a maximum at about 40\ | | c. the reaction is slowest at 0\ | | d. the reaction takes a long time to begin | | | | **13. Which change will increase the speed of the reaction between 1 | | mol of each of the two gases?** | | | | a\. a decrease in surface area of the catalyst | | | | b\. a decrease in temperature | | | | c\. a decrease in the volume of the reaction flask | | | | d\. an increase in the volume of the reaction flask | | | | **14. Magnesium reacts with hydrochloric acid. Which solution would | | give the fastest initial rate of reaction?** | | | | a\. 40g of HCl in 1000cm^3^ of water | | | | b\. 20g of HCl in 1000cm^3^ of water | | | | c\. 10g of HCl in 100cm^3^ of water | | | | d\. 4g of HCl in 50cm^3^ of water | | | | **15. In which reaction is the pressure least likely to affect the | | rate of reaction** | | | | a\. C (s) + CO~2~ (g) \-\--\> 2CO (g) | | | | b\. 2SO2 (g) + O2 (g) \-\--\> 2SO3 (g) | | | | c\. N2 (g) + 3H2 (g) \-\--\> 2NH3 (g) | | | | d\. NaOH (aq) + HCl (aq) \-\--\> NaCl (aq) + H2O (l) | | | | **16. Which of these changes is exothermic?** | | | | a\. evaporation | | | | b\. thermal decomposition | | | | c\. respiration | | | | d\. melting | | | | **17. Which of these changes is endothermic?** | | | | a\. freezing | | | | b\. neutralisation | | | | c\. photosynthesis | | | | d\. combustion | | | | **18. Which element is always present in fuels like coal, oil, and | | natural gas?** | | | | a\. hydrogen | | | | b\. carbon | | | | c\. oxygen | | | | d\. nitrogen | | | | **19. Natural gas burns more easily than other fuels because** | | | | a\. it is more exothermic | | | | b\. it is a gas | | | | c\. it is colourless | | | | d\. it has a low density | | | | **20. Most fuels contain small amounts of sulphur. When they burn, a | | gas which pollutes the atmosphere and causes acid rain is formed. it | | is called** | | | | a\. carbon monoxide | | | | b\. carbon dioxide | | | | c\. sulphur dioxide | | | | d\. sulphur trioxide | | | | **21. Methane (CH~4~) is the main constituent of natural gas. When it | | burns, it produces 890 kJ of heat per mole. How much heat would be | | produced if 64 g of methane were burnt?** | | | | **\[Ar of C = 12, Ar of H = 1\]** | | | | a\. 890 kJ | | | | b\. 1780 kJ | | | | c\. 2670 kJ | | | | d\. 3560 kJ | | | | **22. Which of these reactions would you expect to be endothermic?** | | | | a\. 4K (s) + O~2~ (s) \--\> 2K2O (s) | | | | b\. H2 (g) \--\> 2H (g) | | | | c\. 2NaOH (aq) + H2SO4 (aq) \--\> Na2SO4 (aq) + 2H2O (l) | | | | d\. 2H2 (g) + O2 (g) \--\> 2H2O (l) | | | | **23. An endothermic reaction is one in which** | | | | a\. the reaction vessel gets hot | | | | b\. light is given out | | | | c\. the products contain more energy than the reactants | | | | d\. chemical bonds are made | | | | **24. Which pair of elements, described by their proton number, will | | react together most exothermically?** | | | | a\. 2 and 8 | | | | b\. 12 and 16 | | | | c\. 3 and 10 | | | | d\. 19 and 9 | | | | **25. A fuel is a device for** | | | | a\. converting electrical energy efficiently into chemical energy | | | | b\. converting chemical energy efficiently into electrical energy | | | | c\. recharging accumulators | | | | d\. burning a fuel efficiently | | | | **26. The formation of hydrogen iodide from hydrogen and iodine is an | | endothermic reaction.** | | | | **H-H + I-I \-\--\> H-I + H-I** | | | | **What may be deduced from this information?** | | | | a\. The number of bonds broken is greater than the number of bonds | | formed. | | | | b\. The formation of H-I bonds absorbs energy. | | | | c\. The products possess less energy than the reactants. | | | | d\. The total energy change in bond formation is less than that in | | bond breaking. | | | | **27. Methane gas reacts extremely slowly with air at room | | temperature. If a piece of warm platinum is held in a methane-air | | mixture, the methane ignites. What differences are there between the | | reaction with the platinum and the reaction without the platinum?** | | | | **For the reaction with the platinum:** | | | | **I. The activation energy is lower.** | | | | **II. The energy change is greater.** | | | | **III. The energy of the reactants is higher.** | | | | **IV. The rate of reaction is greater.** | | | | a\. I and II only | | | | b\. I and III only | | | | c\. I and IV only | | | | d\. II and IV only | | | | **28. The graph shows how the total volume of hydrogen produced | | changes when iron fillings reacted with excess dilute sulphuric | | acid.** | | | |  | | | | **Which statement best describes the section PQ of the curve?** | | | | a\. The acid is slowly used up which results in the reaction slowing | | down. | | | | b\. The decreasing mass of the iron filings results in the reaction | | slowing down. | | | | c\. Water is produced in the reaction that dilutes the acid which | | slows down the reaction. | | | | d\. Hydrogen gas produced slows down the reaction. | | | | **29. Two experiments were carried out in which hydrochloric acid was | | added to limestone.** | | | | **Experiment A: 500 cm^3^ of 1.0 mol/dm^3^ hydrochloric acid added to | | an excess of limestone.** | | | | **Experiment B: 100 cm^3^ of 5.0 mol/dm^3^ hydrochloric acid added to | | an excess of limestone.** | | | | **The initial rate of evolution of carbon dioxide and the total | | volume of carbon dioxide evolved were measured in each experiment. | | How do the results in experiment A compare with those in experiment B | | when all other conditions are identical?** | | | |     **    Rate of evolution of carbon dioxide              Total | | volume of carbon dioxide** | | | | a.        It is slower in A than in B.                              | |  It is the same in A and B. | | | | b.        It is faster in B than in A.                                | | It is greater in B than in A. | | | | c.        It is slower in B than in A.                              | |  It is greater in B than in A. | | | | d.        It is the same in A and B.                                | | It is greater in A than in B.     | | | | **30. Why is the reaction H~2~ + Cl~2~ \--\> 2HCl exothermic?** | | | | a\. Energy involved in the bonds breaking is greater than that of | | the bonds forming. | | | | b\. Energy involved in the bonds forming is greater than that of the | | bonds breaking. | | | | c\. More bonds are broken than are formed. | | | | d\. More bonds are formed than are broken.        | | | | MCQ Answers | | | | 1\. c\ | | 2. d\ | | 3. b\ | | 4. b\ | | 5. b\ | | 6. c\ | | 7. a\ | | 8. a\ | | 9. d\ | | 10. a\ | | 11. c (since the total vol of H~2~ collected is about half of X, | | the mass of Zn used should be halved. The steeper gradient of Y | | suggests a faster rate of reaction eg higher temperature)\ | | 12. b | | | | 13\. c | | | | 14\. c | | | | 15\. d (there are no gaseous reactants in the reaction) | | | | 16\. c | | | | 17\. c | | | | 18\. b | | | | 19\. a | | | | 20\. c | | | | 21\. d | | | | 22\. b | | | | 23\. c | | | | 24\. d | | | | 25\. b | | | | 26\. d | | | | 27\. c | | | | 28\. b | | | | 29\. a | | | | 30\. b | | | | *Worked Solutions* | | | | **1. A metallic element forms compounds in which its oxidation states | | are II and III. The element is displaced from solutions of its salts | | by copper.\ | | \ | | a. Using the symbol El for the element, write the formulae for the | | chlorides and oxides of this element.\ | | \ | | chlorides \_\_\_\_\_\_ and \_\_\_\_\_\_\_\_\ | | oxides \_\_\_\_\_\_\_ and \_\_\_\_\_\_\_\_\_\ | | \ | | b. Why is it necessary for the symbols of the majority of the | | elements to consist of two letters rather than one only?\ | | \ | | c. Would you expect this element El to react with dilute sulphuric | | acid? Explain your answer.\ | | \ | | d. Write an equation to show the reduction of an ion of this element | | El from oxidation state III to oxidate state II\ | | **\ | | **[Solution]**\ | | \ | | a. chlorides: ElCl~2~ and ElCl~3\ | | ~oxides: ElO and El~2~O~3\ | | \ | | ~b. There are elements with names that start with the same letter eg. | | copper (Cu) and carbon (C)\ | | \ | | c. No. Because copper does not react with dilute sulphuric acid and | | El is less reactive than copper.\ | | \ | | d. 2El^3+ ^(aq) + Cu (s) \--\> 2El^2+^ (aq) + Cu^2+^ (aq)\ | | \ | | **2. Give one physical property and one chemical property possessed | | by all metals.**\ | | \ | | **[Solution]**\ | | \ | | a. good conductor of electricity/heat\ | | \ | | b. form oxides which show basic properties\ | | \ | | **3. At 150^o^C and a pressure of one atmosphere, the reversible | | reaction between gas A and gas B reaches a dynamic equilibrium.\ | | \ | | A (g) + 2B (g) \ AB~2~ (g) : heat change = -220kJ/mol\ | | \ | | a. Is the formation of AB~2 ~exothermic or endothermic? Explain your | | answer.\ | | \ | | bi. What is meant by the phrase dynamic equilibrium?\ | | \ | | bii. Predict how the proportion of AB~2 ~at equilibrium changes if | | the pressure is increased.\ | | \ | | c. What effect will an increase in temperature have on the rate of | | formation of AB~2~? Explain your answer in terms of the movement of | | the molecules.**\ | | \ | | **[Solution]**\ | | \ | | a. exothermic. This is because the forward reaction has a negative | | heat change, indicating that heat is released.\ | | \ | | bi. The amounts of A, B and AB~2~ are constant (equilibrium) but the | | forward and backward reactions are still taking place (dynamic).\ | | \ | | bii. amount of AB~2 ~increases\ | | \ | | c. Rate is faster. At higher temperature, the molecules have more | | kinetic energy. More molecules possess energy greater than the | | required minimum energy for a reaction to take place. Furthermore, | | they collide more frequently with one another. Hence, the rate of | | reaction increases.\ | | \ | | **4. The element oxygen exists in two forms, O~2~ and O~3~. Both | | forms are gases.\ | | \ | | ai. Ozone molecules O~3~ decompose when heated into O2 molecules. | | Construct the equation for this decomposition.\ | | \ | | aii. What volume of oxygen O~2~ is formed when 40cm3 of ozone O~3~ is | | decomposed, both volumes being measured at the same temperature and | | pressure?\ | | \ | | b. Ozone is an oxidizing agent. Describe the color change you expect | | to see when ozone is bubbled into aqueous potassium iodide.\ | | \ | | color before:\ | | color after:**\ | | \ | | **[Solution]**\ | | \ | | ai. O~3~ (g) \--\> 3/2 O~2~ (g)\ | | \ | | aii. 60 cm^3^\ | | \ | | bi. colorless\ | | \ | | bii. brown\ | | **\ | | 5a. Ammonia is made in the Haber process by the reversible reaction | | between nitrogen and hydrogen.\ | | \ | | i. How is nitrogen obtained from liquid air for use in this process?\ | | \ | | ii. State the name of the catalyst and the conditions used in the | | Haber process.\ | | \ | | b. Ethanol can be manufactured by reacting ethene and steam in the | | presence of phosphoric acid as a catalyst.\ | | \ | | The reaction is reversible and forms an equilibrium mixture.\ | | \ | | C~2~H~4~ (g) + H~2~O \ C~2~H~5~OH (g)\ | | \ | | i. Predict how increasing the pressure will change the percentage of | | ethanol present at equilibrium. Explain your answer.\ | | \ | | ii. The table shows how the percentage of ethanol present at | | equilibrium changes with temperature at a pressure of 60 | | atmospheres.** | | | | ** temperature/^o^C** ** percentage of ethanol produce/%** | | ----------------------- -------------------------------------- | | ** 200** ** 49** | | ** 260** ** 38** | | ** 320** ** 34** | | | | **\ | | Is the formation of ethanol exothermic or endothermic? Explain your | | answer.\ | | \ | | c. One use of ethanol is the manufacture of an acid. Name the acid | | and draw its structural formula.**\ | | \ | | **[Solution]**\ | | \ | | ai. fractional distillation\ | | \ | | aii. iron(III) oxide catalyst at 450^o^C and 200 atm\ | | \ | | bi. Increasing pressure will shift the equilibrium to the right where | | there is a reduction in total amount of gases since 2 moles of gases | | combine to give only 1 mole. Hence, the percentage of ethanol | | increases.\ | | \ | | bii. As temperature increases, amount of ethanol produced decreases, | | showing that the reverse reaction is favored. Hence, the backward | | reaction is endothermic where heat is absorbed. Therefore, the | | formation of ethanol is exothermic.\ | | \ | | c. ethanoic acid | | | | http://www.gcestudybuddy.com/\_/rsrc/1306572051962/chemistry-classroo | | m/rate-of-reactions/Screen%20shot%202011-05-28%20at%20PM%2004.40.41.p | | ng?height=135&width=200 | | | | **6. The table below shows some bond energies, measured in kilojoules | | per mole. Bond energy is the energy required to break the bonds | | between pairs of atoms** | | | | ** bond** **bond energy in kJ/mol    ** **bond ** **bond | | energy in kJ/mol** | | ------------ ------------------------------- -------------- ------- | | -------------------- | | **H - H** **436     ** **Cl - Cl ** **242 * | | * | | **H - Cl** **431 ** **C - H ** **412 * | | * | | **C = C** **612 ** **C - C ** **348 * | | * | | **N = N** **409 ** **N - N ** **163 * | | * | | | | **a. Which of the bonds listed above is the strongest?** | | | | **b. Is the double bond between two carbon atoms twice as strong as a | | single bond? Use the info given above to explain your answer** | | | | **c. Use the info given to calculate the total energy required to | | break one mole of methane into atoms.** | | | | **CH~4~ \--\> C + 4H; ∆H = ? kJ** | | | | **d. Bond-making is an exothermic process (∆H, -ve)** | | | | **Complete the statements below to calculate the energy change | | expected from the reaction of one mole of hydrogen with one mole of | | chlorine to form two moles of hydrogen chloride** | | | | **H~2~ + Cl~2~ \--\> 2HCl; ∆H = ? kJ** | | | | **Energy change in breaking the bonds in one mole of H2 = | | \_\_\_\_\_\_kJ** | | | | **Energy change in breaking the bonds in one mole of Cl2 | | = \_\_\_\_\_\_kJ** | | | | **Total energy change = \_\_\_\_\_\_kJ** | | | | **Energy change in making the bonds in two moles of HCl | | = \_\_\_\_\_\_kJ** | | | | **Hence ∆H for this reaction = \_\_\_\_\_\_kJ** | | | | **[Solution]** | | | | 6a. C = C bond | | | | 6b. No. If C = C bond is twice as strong as a C - C bond, then the C | | = C bond energy should be 2 x 348 = 696 kJ/mol, but the bond energy | | of C = C bond is actually less than that. | | | | 6c. 4 x 412 = 1648 kJ | |