Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Unit
Physical Chemistry
442 practice questions
Topics covered
Practice questions
421–430 of 442
Question 421
6 marks · Normal
Answer and see the solution →Hydrogen iodide is formed in a reversible reaction:
(a)[3 marks]Explain, in terms of exothermic and endothermic reactions, what happens to the position of equilibrium if the temperature is decreased.
(b)[3 marks]Explain why adding a catalyst to the sealed reaction vessel does not change the position of equilibrium.
Question 422
6 marks · Normal
Answer and see the solution →Consider the equilibrium:
(a)[2 marks]State whether the forward reaction is exothermic or endothermic. Give a reason based on the value of ΔH.
(b)[2 marks]Predict and explain what happens to the amount of PCl₃(g) at equilibrium if the temperature is increased.
(c)[2 marks]State whether adding a catalyst affects the amount of PCl₃(g) present at equilibrium. Explain your answer.
Question 423
8 marks · Hard
Answer and see the solution →This question is about an industrial process involving a reversible reaction in a sealed vessel:
At dynamic equilibrium, the concentrations of all four gases remain constant. The process operator wants to maximise the production of C.
(a)[2 marks]State two characteristics of a reaction mixture at dynamic equilibrium. Explain why both these characteristics occur.
(b)[2 marks]The operator increases the concentration of A. Predict and explain how the position of equilibrium will change, and what effect this has on the yield of C.
(c)[2 marks]If the concentration of D is continuously removed from the vessel as it forms, explain (i) how the position of equilibrium will change, and (ii) what will happen to the rate of the forward and reverse reactions immediately after removal.
(d)[2 marks]Suggest one reason, based on the above equilibrium, why controlling concentrations is important in industrial chemical processes.
Question 424
8 marks · Hard
Answer and see the solution →An experiment is set up in a sealed container for the reaction below, which can reach dynamic equilibrium:
The concentrations of all substances are measured over time.
(a)[2 marks]Describe the conditions required for the system to reach dynamic equilibrium. Explain why these conditions are necessary.
(b)[2 marks]The concentration of EF increases while E2 and F2 decrease for some time, then all concentrations level off. Explain what this shows about the rate of the forward and reverse reactions at this point.
(c)[2 marks]If more F2 is added to the system at equilibrium, predict and explain what happens to the concentrations of E2, F2, and EF before the system settles at the new equilibrium.
(d)[2 marks]Explain, in terms of equilibrium, why increasing the concentration of F2 can help industries to increase the yield of EF in this reaction.
Question 425
7 marks · Hard
Answer and see the solution →Consider the industrial reaction below, carried out in a sealed vessel:
This reaction can reach dynamic equilibrium. The mixture initially contains only X.
(a)[2 marks]Describe what happens to the concentration of X as the system approaches equilibrium. Explain your answer.
(b)[2 marks]At equilibrium, more X is added. Predict what will happen to the concentrations of Y and Z and explain your answer in terms of the position of equilibrium.
(c)[1 mark]Suggest one reason why maintaining constant concentrations of products in continuous industrial reactions is important.
(d)[2 marks]Explain, using the idea of equilibrium, what would happen to the rate of the forward and reverse reactions immediately after X is added, until the new equilibrium is reached.
Question 426
7 marks · Easy
Answer and see the solution →A student investigates the thermal decomposition of ammonium chloride in an open dish and a sealed container.
(a)[2 marks]Explain why changing the pressure has little effect on the rate of the decomposition when ammonium chloride is heated as a solid in an open dish.
(b)[2 marks]Write a balanced chemical equation, using the correct symbol, to show that the thermal decomposition of ammonium chloride is a reversible reaction.
(c)[1 mark]If the experiment is repeated in a sealed container, what substances will be present when equilibrium is reached? Give your answer as a list.
(d)[2 marks]Explain why all these substances are present at equilibrium, even though the reaction appears to have stopped.
Question 427
7 marks · Easy
Answer and see the solution →This question is about catalysts and dynamic equilibrium.
(a)[1 mark]State what is meant by a catalyst.
(b)[2 marks]Describe how you could show that manganese(IV) oxide is a catalyst in the decomposition of hydrogen peroxide.
(c)[2 marks]Define dynamic equilibrium in a reversible reaction.
(d)[2 marks]Explain why the concentrations of reactants and products remain constant at dynamic equilibrium, although both reactions are still occurring.
Question 428
7 marks · Easy
Answer and see the solution →This question is about the interpretation of reaction profile diagrams and the properties of equilibrium.
(a)The diagram below shows an energy profile for a reaction without a catalyst.
Reaction profile diagram for an exothermic reaction (no catalyst). (i)[2 marks]Draw on the diagram a line to show how the profile changes when a catalyst is used. Label the activation energy for the catalysed reaction.
(ii)[1 mark]Explain why the overall enthalpy change (ΔH) for the reaction does not change when a catalyst is used.
(b)[2 marks]In a reversible reaction at equilibrium, the following is observed: the concentrations of reactants and products stay the same, even though both the forward and reverse reactions are occurring. Explain why the concentrations remain unchanged at equilibrium, but the reaction is still said to be 'dynamic'.
(c)[2 marks]A student suggests that adding a catalyst will increase the amount of product at equilibrium. Do you agree? Explain your answer.
Question 429
7 marks · Easy
Answer and see the solution →A student investigates the effect of a possible catalyst on the reversible reaction shown below, carried out in a sealed container:
She wishes to know whether the substance speeds up the reaction, and how changes in pressure affect the amount of SO3 at equilibrium.
(a)[3 marks]Describe a method you would use to show that a substance is a catalyst in this reaction.
(b)[2 marks]Explain what is meant by 'the position of equilibrium' for this reaction.
(c)[2 marks]Predict and explain the effect of increasing pressure on the position of equilibrium of this reaction.
Question 430
7 marks · Easy
Answer and see the solution →A student carries out an experiment to investigate the effect of surface area on the rate of reaction between excess powdered calcium carbonate and 50 cm³ of hydrochloric acid at 2.00 mol/dm³. The loss in mass, due to carbon dioxide being produced, is measured every 30 seconds. The experiment uses a conical flask as shown.
(a)[2 marks]Describe how you could carry out this experiment to measure the rate of carbon dioxide production.
(b)In a second experiment, the student repeats the reaction using the same amount of powdered calcium carbonate and acid, but keeps the flask sealed with a stopper and a delivery tube connected to an inverted measuring cylinder filled with water, to collect the gas formed.
The volume of carbon dioxide produced in the first minute is 45 cm³.
(i)[1 mark]Calculate the average rate of reaction (in cm³/s) for the first minute.
(ii)[1 mark]State one way in which the method used in this experiment allows the rate to be measured more accurately than using just a balance.
(c)[3 marks]The student then investigates the following gas-phase reversible reaction in a sealed container:
Predict and explain how increasing the pressure will affect the position of equilibrium of this reaction.