The Rate and Extent of Chemical ChangeAQA GCSE Chemistry: Topic test

20 questions, 54 marks

AQA GCSE Chemistry

The Rate and Extent of Chemical Change topic test

Total 54 marks

Name

Class

Date

1
A pharmacist is testing how quickly an effervescent vitamin C tablet dissolves and reacts with water at different temperatures. She drops an identical tablet into 100 cm3 of water at 20°C, 40°C and 60°C, and times how long it takes for the tablet to completely disappear and stop fizzing at each temperature.
(a)
Which row correctly shows how the rate of reaction and the time taken for the tablet to disappear change as the water temperature increases from 20°C to 60°C?
[1 mark]
ARate increases; time taken decreases
BRate increases; time taken increases
CRate decreases; time taken decreases
DRate decreases; time taken increases
(b)
Using collision theory, why does the reaction proceed faster in the 60°C water than in the 20°C water?
[1 mark]
AThe particles are more crowded together at higher temperature
BThe particles have more kinetic energy, so they collide more often and more collisions have enough energy to react
CThe tablet becomes a different substance at higher temperature
DHigher temperature increases the concentration of the water
(c)
Suggest and explain one change to the tablet itself (not the water) that would increase the rate of the reaction, other than changing temperature.
[2 marks]
Total for question 1: 4 marks
2
A biology technician demonstrates enzyme catalysis to a chemistry class. She adds a small piece of raw liver, which contains the enzyme catalase, to a test tube of hydrogen peroxide solution, and compares the rate of bubbling with a second test tube of hydrogen peroxide solution with no liver added. Hydrogen peroxide decomposes to form water and oxygen: 2H2O2 -> 2H2O + O2.
(a)
What is the role of the catalase in the liver in this reaction?
[1 mark]
AIt is used up and forms part of the products
BIt reacts with the oxygen produced to slow the reaction
CIt acts as a biological catalyst, increasing the rate of decomposition without being used up
DIt cools the reaction mixture, slowing the rate
(b)
How could the student confirm that the gas produced in the test tube containing liver is oxygen?
[1 mark]
ATest it with damp litmus paper and check it turns white
BTest it with limewater and check it turns milky
CHold a lit splint at the mouth of the tube and listen for a pop
DInsert a glowing splint into the test tube and check it relights
(c)
Explain, in terms of activation energy, why the reaction in the test tube with liver produces bubbles of gas much faster than the test tube without liver, even though both tubes are at the same temperature.
[2 marks]
Total for question 2: 4 marks
3
A laboratory technician demonstrates a reversible reaction by gently heating solid ammonium chloride in one end of a sealed glass tube. White fumes form and collect as a white solid near the cooler end of the tube. The reaction is: NH4Cl(s) ⇌ NH3(g) + HCl(g).
(a)
Explain, in terms of particles and energy, what happens to the ammonium chloride at the heated end of the tube, and why the white solid then reforms at the cooler end.
[3 marks]
(b)
State what is meant by a reversible reaction, and explain why this demonstration shows that the breakdown of ammonium chloride is a reversible reaction rather than an irreversible one.
[4 marks]
Total for question 3: 7 marks
4
A chemical engineer at a plastics manufacturer is studying a general gas-phase equilibrium reaction used in one stage of production: 2X(g) + Y(g) ⇌ 2Z(g). The forward reaction is exothermic. The engineer wants to predict how changing the reaction conditions would affect the position of equilibrium and the rate at which equilibrium is reached, in order to choose sensible operating conditions for a new reactor.
(a)
State and apply Le Chatelier's Principle to predict, with reasons, the effect on the position of this equilibrium of (i) increasing the pressure and (ii) increasing the temperature.
[6 marks]
(b)
The engineer is also considering adding a catalyst to the reactor. Explain the effect a catalyst would have on the rate of this reaction and on the position of the equilibrium, and evaluate, given your answers to part (a), why a real industrial reactor might still use conditions of only moderately high pressure and moderate temperature rather than the highest possible pressure and lowest possible temperature suggested by equilibrium position alone.
[6 marks]
Total for question 4: 12 marks
5
A student investigates how quickly an indigestion tablet neutralises excess acid by reacting a whole tablet, and separately a crushed (powdered) sample of an identical tablet, with the same volume and concentration of dilute hydrochloric acid at the same temperature. She measures the volume of gas released over time using a gas syringe in each case.
(a)
Which property of the crushed tablet explains why it is expected to react faster than the whole tablet?
[1 mark]
AThe crushed tablet has a greater total surface area in contact with the acid
BThe crushed tablet has a smaller total mass
CThe crushed tablet is a different chemical to the whole tablet
DThe crushed tablet has a lower concentration
(b)
The student plots a graph of the volume of gas produced against time for both experiments. Compared with the whole tablet, what would the graph for the crushed tablet be expected to show?
[1 mark]
AA shallower initial slope and a lower final volume of gas
BA steeper initial slope, reaching the same final volume of gas sooner
CA steeper initial slope but a lower final volume of gas
DAn identical graph, since the same mass of tablet and acid are used
(c)
The student's teacher suggests repeating the experiment using a much greater concentration of hydrochloric acid, keeping everything else the same. Predict, using collision theory, what effect this would have on the rate of reaction.
[2 marks]
Total for question 5: 4 marks
6
A food manufacturer produces margarine by reacting vegetable oil with hydrogen gas in the presence of a nickel catalyst, which converts some of the carbon-carbon double bonds in the oil into single bonds, making the fat more solid at room temperature. The manufacturer compares using the nickel catalyst as coarse granules with using it as a fine powder, both at the same total mass of nickel.
(a)
What effect does using the nickel catalyst as a fine powder, rather than coarse granules, have on the rate of the reaction, and why?
[1 mark]
ANo effect, because the total mass of catalyst is the same in each case
BThe reaction is slower, because the powdered catalyst reacts with and is used up by the oil
CThe reaction is faster, because the powdered catalyst has a greater surface area exposed to the oil and hydrogen
DThe reaction is faster, because the powdered catalyst raises the temperature of the mixture
(b)
Which statement correctly describes how the nickel catalyst increases the rate of the hydrogenation reaction?
[1 mark]
AIt increases the concentration of hydrogen in the mixture
BIt reacts with the oil to form a new catalyst each time
CIt increases the temperature needed for the reaction to start
DIt provides a reaction pathway with a lower activation energy
(c)
After the reaction, the manufacturer filters the mixture to recover the nickel catalyst and reuses it in the next batch of margarine. Explain why this is possible.
[2 marks]
Total for question 6: 4 marks
7
A confectionery flavourings company produces methyl propanoate, the ester responsible for apple flavour, by reacting methanol with propanoic acid in a reversible esterification: methanol + propanoic acid ⇌ methyl propanoate + water.
(a)
State what is meant by the term 'reversible reaction', and explain what is meant by 'dynamic equilibrium' when this reaction reaches equilibrium in a sealed container.
[3 marks]
(b)
Explain why, even after the reaction has been left for a long time in the sealed container, the company never obtains a pure sample of methyl propanoate directly from the reaction mixture, and state what this tells you about the relative amounts of reactants and products present at equilibrium.
[4 marks]
Total for question 7: 7 marks
8
A pharmaceutical company runs a reversible reaction to manufacture an intermediate drug compound: P(g) + Q(g) ⇌ 2R(g), where the forward reaction is endothermic. Chemists at the company are investigating how to reach equilibrium faster and how to increase the equilibrium yield of R.
(a)
Explain, using collision theory, how (i) increasing the temperature and (ii) adding a catalyst would each increase the rate of this reaction, making clear the difference between how each one works.
[6 marks]
(b)
The forward reaction P(g) + Q(g) ⇌ 2R(g) is endothermic. Predict and explain, using Le Chatelier's Principle, the effect on the equilibrium yield of R of (i) decreasing the temperature and (ii) changing the pressure, given that there are equal numbers of gas moles on each side of the equation.
[6 marks]
Total for question 8: 12 marks

End of questions