Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Unit
Physical Chemistry
442 practice questions
Topics covered
Practice questions
61–70 of 71 · Hard
Question 61
2 marks · Hard
Answer and see the solution →A chemist adds a catalyst to a reversible reaction mixture at equilibrium. The student expects the concentration of products to increase once the catalyst is added.
Explain, with a reason, whether the student's expectation is correct.
Question 62
5 marks · Hard
Answer and see the solution →A student investigates the following reversible reaction at equilibrium: \[ \ce{CO(g) + H2O(g) \rightleftharpoons CO2(g) + H2(g)} \] The student adds a catalyst to the closed reaction vessel.
(a)State what happens to: (i) the rate at which equilibrium is reached (ii) the position of equilibrium after the catalyst is added.
(i)[1 mark]the rate at which equilibrium is reached
(ii)[1 mark]the position of equilibrium
(b)[3 marks]Explain, with reasons, why a catalyst does or does not affect the position of equilibrium in a reversible reaction. Include reference to the rates of the forward and reverse reactions in your answer.
Question 63
2 marks · Hard
Answer and see the solution →Explain why the addition of a catalyst does not affect the position of equilibrium in a reversible reaction.
Question 64
2 marks · Hard
Answer and see the solution →The following reversible reaction is at equilibrium in a sealed container:
State and explain the effect on the position of equilibrium if additional Y(g) is added to the system.
Question 65
5 marks · Hard
Answer and see the solution →The reaction below is at equilibrium in a closed vessel:
A student increases the concentration of P(g).
(a)[1 mark]Predict the effect on the position of equilibrium. State your answer as 'left', 'right' or 'no change'.
(b)[2 marks]Explain your answer in (a), referring to the effect of changing concentration.
(c)[2 marks]If instead some M(g) is removed from the vessel, what effect would this have on the equilibrium position? State your answer and explain.
Question 66
2 marks · Hard
Answer and see the solution →For the equilibrium reaction below:
Explain, in terms of concentration, what happens to the position of equilibrium if some B(g) is removed from the mixture.
Question 67
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 68
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 69
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 70
9 marks · Hard
Answer and see the solution →This question is about bond energies and equilibrium in a sealed container.
(a)[2 marks]The reaction below shows the thermal decomposition of calcium carbonate, which is carried out in a sealed container:
Explain what is meant by a 'sealed container' in the context of this reversible reaction. [2]
(b)[2 marks](i) State whether the decomposition of calcium carbonate is an exothermic or endothermic process. Give a reason for your answer, including a statement about bond making or breaking. [2]
(b)[3 marks](ii) The following bond energies can be used to estimate the enthalpy change (ΔH) for the reaction:
Mean bond energies Bond Bond energy / kJ mol⁻¹ C=O (in CO2) 805 C–O (in CaCO3) 745 O–Ca (in CaCO3) 350 The reaction is: Assume that 1 mole of calcium carbonate decomposes. Use the bond energies above to estimate the enthalpy change (ΔH) for the decomposition of calcium carbonate. Show your working. [3]
(c)[2 marks]State and explain what would happen to the position of equilibrium if some carbon dioxide is removed from the sealed container once equilibrium is established. [2]