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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.
B. Measuring change in mass of reaction mixture.
Speed of catalysed reactions can be increased by:
Characteristics of enzymes:
H2 (g) + Br2 (g) → 2HBr (g)
Bonds of H2 and Br2 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
= the bond energy of 2 H – Br bonds
= – 732 kJ
= 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.
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.
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.
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 H2 + Cl2 --> 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 100cm3 of 1mol/dm3 aqueous hydrogen peroxide, catalysed by manganese(IV) oxide.
2H2O2 (aq) --> 2H2O (l) + O2 (g)
a. adding some 0.1 mol/dm3 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.
N2 (g) + 3H2 (g) <---> 2NH3 (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?
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 30oC.
a. using 1.0 g of powdered zinc at 20oC
b. using 1.0 g of granulated zinc at 20oC
c. using 0.5 g of granulated zinc at 40oC
d. using 0.5 g of granulated zinc at 20oC
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.
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 1000cm3 of water
b. 20g of HCl in 1000cm3 of water
c. 10g of HCl in 100cm3 of water
d. 4g of HCl in 50cm3 of water
15. In which reaction is the pressure least likely to affect the rate of reaction
a. C (s) + CO2 (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?
b. thermal decomposition
17. Which of these changes is endothermic?
18. Which element is always present in fuels like coal, oil, and natural gas?
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 (CH4) 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) + O2 (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 cm3 of 1.0 mol/dm3 hydrochloric acid added to an excess of limestone.
Experiment B: 100 cm3 of 5.0 mol/dm3 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 H2 + Cl2 --> 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.
11. c (since the total vol of H2 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)
15. d (there are no gaseous reactants in the reaction)
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
a. chlorides: ElCl2 and ElCl3
oxides: ElO and El2O3
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. 2El3+ (aq) + Cu (s) --> 2El2+ (aq) + Cu2+ (aq)
2. Give one physical property and one chemical property possessed by all metals.
a. good conductor of electricity/heat
b. form oxides which show basic properties
3. At 150oC and a pressure of one atmosphere, the reversible reaction between gas A and gas B reaches a dynamic equilibrium.
A (g) + 2B (g) <---> AB2 (g) : heat change = -220kJ/mol
a. Is the formation of AB2 exothermic or endothermic? Explain your answer.
bi. What is meant by the phrase dynamic equilibrium?
bii. Predict how the proportion of AB2 at equilibrium changes if the pressure is increased.
c. What effect will an increase in temperature have on the rate of formation of AB2? Explain your answer in terms of the movement of the molecules.
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 AB2 are constant (equilibrium) but the forward and backward reactions are still taking place (dynamic).
bii. amount of AB2 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, O2 and O3. Both forms are gases.
ai. Ozone molecules O3 decompose when heated into O2 molecules. Construct the equation for this decomposition.
aii. What volume of oxygen O2 is formed when 40cm3 of ozone O3 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.
ai. O3 (g) --> 3/2 O2 (g)
aii. 60 cm3
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.
C2H4 (g) + H2O <--> C2H5OH (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.
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.
ai. fractional distillation
aii. iron(III) oxide catalyst at 450oC 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
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
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.
CH4 --> 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
H2 + Cl2 --> 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
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
6di. 436 kJ
6dii. 242 kJ
1diii. 436 + 242 = 678 kJ
1div. -(2 x 431) = - 862 kJ
1dv. 678 + (- 862) = - 184 kJ
7. In the Contact process for the manufacture of sulphuric acid, sulphur dioxide is converted into sulphur dioxide.
2SO2 (g) + O2 (g) <---> 2SO3 (g) ∆H = - 98 kJ/mol
a. The reaction reaches a dynamic equilibrium. Explain the term.
b. A mixture of sulphur dioxide, oxygen, and sulphur trioxide was allowed to reach equilibrium, then the temperature was raised. Predict the effect of raising the temperature on
i. the composition of the equilibrium mixture
ii. the rate of reaction
Explain your answers.
c. Describe how you would prepare a pure dry sample of sodium sulphate starting with dilute sulphuric acid.
7a. At dynamic equilibrium for a reversible reaction, the forward rate of reaction is equal to the backward rate of reaction, and both rates are not equal to zero.
7bi. Amount of SO3 decreases. When temperature is raised, the equilibrium shifts to the left where heat is absorbed (backward reaction is endothermic) so as to counteract the temperature change.
7bii. Faster rate of reaction. Since temperature is raised, both forward and backward rates of reaction are increased.
7c. First, perform a titration on 25.0 cm3 of aqueous NaOH, with dilute sulphuric acid using a suitable indicator such as phenolphthalein. The volume of acid used is noted at the end point when the colour of the indicator changes. Repeat the experiment but without the indicator. The final solution will be sodium sulphate solution. Crystalise sodium sulphate by evaporation. The crystals are filtered, washed with water, and dried with filter paper and dessicator.
8. In the future, fuel cells may be used to power cars. In a fuel cell, the overall reaction is represented by the equatin
2H2 (g) + O2 (g) --> 2H2O (l)
a. This is the energy profile diagram for the above reaction
i. Label on the diagram the activation energy of the reaction.
ii. The fuel cell contains a catalyst. Draw a second curve on the diagram to show the energy profile for the catalysed reaction.
iii. Explain why this reaction is exothermic in terms of bond breaking and bond forming.
b. Choose from the following list the metal that is most likely to act as a catalyst. Give a reason for your answer.
CH4 + 2O2 -------> CO2 + 2H2O
a. Explain why this reaction is exothermic in terms of the energy changes that take place during bond breaking and bond forming.
b. Calculate the energy released when 4.0g of methane is completely combusted.
c. Draw the energy profile diagram for the complete combustion of methane.
9a. The reaction is exothermic because the heat of reaction, ∆H, has a negative value. The energy released during formation of covalent bonds in products is greater than the energy absorbed to break covalent bonds in reactants. Hence, the overall reaction is exothermic. A total of 890 kJ of energy is released.
9b. Mr of CH4 = 16
No. of mol of CH4 = 4/16 = 0.25
Energy released = 0.25 x 890 = 225 kJ
10. Methane is a fuel. It completely burns to form carbon dioxide and water. When 1 mole of methane is burned, 890 kJ of energy is released.
a. Calculate the energy released when 0.32g of methane is burned.
b. Use ideas of bond breaking and bond forming to explain why the reaction exothermic.
10a. 0.32g of methane contains 0.32/16 = 0.020 moles of methane
energy released = 0.02 x 890 = 17.8 kJ
10b. The energy released by formation of bonds in carbon dioxide and water is far greater than the energy absorbed to break bonds in methane and the oxygen molecules.
11. Hydrogen is used as a fuel in some space rockets.
a. Describe how hydrogen is manufactured from a named hydrocarbon source.
b. A highly exothermic reaction occurs between hydrogen as oxygen to form water.
i. Suggest why liquid hydrogen, rather than hydrogen gas is carried by space rockets.
ii. Explain what is meant by an exothermic reaction.
iii. Which bonds are broken in this reaction.
iv. What type of energy change occurs when bonds are formed?
v. When 1 mole of hydrogen molecules reacts with oxygen, the energy ÔH = -285kJ
Calculate the energy change which occurs when 100g of hydrogen reacts with oxygen.
11a. Hydrogen is formed from the reaction between steam and methane.
H2O (g) + CH4 (g) --> CO (g) + 3H2 (g)
bi. Liquid hydrogen occupies a smaller volume and so is easier to transport.
bii. Exothermic reactions are those where heat energy is released in the course of the reaction.
biii. H-H and O=O bonds
biv. Heat is released. Chemical energy is converted into heat energy, sometimes with the emission of light.
bv. 100g of H contains 100/2 = 50 moles of H
Energy changes = 50(-285) = -14250kJ