The Rate & Extent of Chemical ChangeOxford AQA IGCSE Chemistry: Topic test

20 questions, 54 marks

Oxford AQA IGCSE Chemistry

The Rate & Extent of Chemical Change topic test

Total 54 marks

Name

Class

Date

1
A group of students investigates the rate of reaction between a coil of magnesium ribbon and excess dilute nitric acid by collecting the hydrogen gas produced using a gas syringe. In the first 40 seconds of the reaction, 48 cm3 of gas is collected.
(a)
Calculate the mean rate of reaction over the first 40 seconds, in cm3/s.
[1 mark]
A1.2 cm3/s
B0.83 cm3/s
C8.3 cm3/s
D12 cm3/s
(b)
What happens to the rate of gas production as the reaction proceeds and the acid becomes used up, assuming the magnesium remains in excess?
[1 mark]
AIt stays constant
BIt decreases
CIt increases
DThe reaction stops immediately
(c)
Explain, in terms of particle collisions, why the rate of reaction decreases as the acid becomes more dilute (used up) during the experiment.
[2 marks]
Total for question 1: 4 marks
2
A teacher demonstrates burning a sample of natural gas: the gas reacts explosively with oxygen once ignited, releasing a large amount of energy, but is completely unreactive with the oxygen around it at room temperature until a spark or flame is applied.
(a)
Why does the natural gas not react with the surrounding oxygen at room temperature, even though the reaction is highly exothermic once started?
[1 mark]
AThe gas is not flammable enough
BOxygen is not present in sufficient concentration
CThe reacting particles do not usually collide with enough energy to overcome the activation energy required
DThe particles are moving too fast at room temperature
(b)
What does the spark or flame provide that allows the reaction to begin?
[1 mark]
AIt removes the oxygen
BIt cools the particles down
CIt changes the products formed
DIt provides enough energy for particles to react with the required activation energy
(c)
Define activation energy, and explain what must happen for two particles to react successfully according to collision theory.
[2 marks]
Total for question 2: 4 marks
3
A company tests a new catalyst for the industrial production of a chemical by comparing the time taken for a fixed amount of reactant to be used up, with and without the catalyst present, at the same temperature and using the same concentration of reactants.
(a)
Explain what is meant by a catalyst, and state one industrial benefit of using catalysts in chemical processes.
[3 marks]
(b)
The company also tests how increasing the temperature, and separately how increasing the concentration of the reactant solution, each affect the rate of the same reaction without the catalyst. Explain, using collision theory, why both of these changes increase the rate of reaction.
[4 marks]
Total for question 3: 7 marks
4
A school science department is planning the required practical to investigate how surface area affects the rate of reaction between calcium carbonate and dilute hydrochloric acid, using calcium carbonate in three different forms: large chips, small chips, and powder, with everything else kept the same.
(a)
Describe a suitable method the department could use to investigate how surface area affects the rate of this reaction, including how the rate would be measured and what should be kept constant for a fair test.
[6 marks]
(b)
The department's results show that the powdered calcium carbonate produced 48 cm3 of gas in the first 20 seconds, while the large chips produced only 12 cm3 of gas in the same 20 seconds. Calculate the mean rate of reaction for each form over this period, and explain, using collision theory, why the powder reacts faster than the large chips.
[6 marks]
Total for question 4: 12 marks
5
A student is given a sealed tube containing a mixture of hydrated and anhydrous copper sulfate at equilibrium, and is asked to predict what happens if the sealed tube is opened to the air.
(a)
What is a reversible reaction?
[1 mark]
AA reaction that only occurs in one direction
BA reaction that requires a catalyst
CA reaction that cannot reach equilibrium
DA reaction in which the products can react to reform the original reactants
(b)
In the hydrated ⇌ anhydrous copper sulfate reaction, which direction is endothermic?
[1 mark]
AThe forward reaction (hydrated to anhydrous, releasing water)
BThe reverse reaction (anhydrous to hydrated)
CBoth directions are endothermic
DNeither direction involves an energy change
(c)
Explain what is meant by dynamic equilibrium in a reversible reaction occurring in a closed system.
[2 marks]
Total for question 5: 4 marks
6
A student studies the reaction between magnesium and copper(II) oxide, Mg + CuO -> MgO + Cu, and separately writes the ionic equation for the reaction between magnesium metal and copper(II) ions in solution: Mg + Cu2+ -> Mg2+ + Cu.
(a)
In the reaction Mg + CuO -> MgO + Cu, which substance is reduced?
[1 mark]
AMagnesium, because it gains oxygen
BCopper(II) oxide, because it loses oxygen
CMagnesium, because it loses oxygen
DCopper(II) oxide, because it gains oxygen
(b)
In the ionic equation Mg + Cu2+ -> Mg2+ + Cu, what has happened to the magnesium in terms of electrons?
[1 mark]
AIt has gained two electrons
BIt has gained one electron
CIt has lost two electrons
DNo electrons have transferred
(c)
State the definitions of oxidation and reduction in terms of electrons, and use them to explain why this reaction is called a redox reaction.
[2 marks]
Total for question 6: 4 marks
7
A food-packaging company studies a reversible gas-phase equilibrium reaction used to generate a preservative gas inside sealed packaging: 3G(g) ⇌ H(g), where the forward reaction (forming H) is exothermic.
(a)
State what happens to the position of equilibrium, and to the yield of H, if the temperature of this system is increased.
[3 marks]
(b)
State and explain what happens to the yield of H if the pressure of the system is increased instead, referring to the number of gas molecules on each side of the equation.
[4 marks]
Total for question 7: 7 marks
8
An industrial chemist is comparing the conditions used in the Haber process (making ammonia) with those used in the Contact process (making sulfuric acid), and is asked to justify why each process uses the specific temperature and pressure it does.
(a)
Describe the raw materials, conditions and reversible equation for the Haber process, and explain why a compromise temperature of around 450°C, rather than a much lower temperature, is used, given that the forward reaction is exothermic.
[6 marks]
(b)
Describe the three stages of the Contact process, and explain why Stage 2 uses only a moderate temperature (around 450°C) and atmospheric, rather than very high, pressure, despite higher pressure increasing the equilibrium yield of sulfur trioxide.
[6 marks]
Total for question 8: 12 marks

End of questions