Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Unit
Physical Chemistry
442 practice questions
Topics covered
Practice questions
31–40 of 71 · Hard
Question 31
2 marks · Hard
Answer and see the solution →A chemical reaction between nitrogen and hydrogen gases is taking place in a sealed vessel. The pressure inside the vessel is increased while the temperature remains constant.
Describe and explain what happens to the rate of reaction when the pressure is increased.
Question 32
5 marks · Hard
Answer and see the solution →A student investigates the effect of pressure on two reactions:
(a)[3 marks]Reaction 1: Two solid powders are mixed together in a sealed container. Predict what happens to the rate of reaction if the pressure is increased. Explain your answer using particle theory.
(b)[2 marks]Reaction 2: Two liquids are mixed together. Explain, using your knowledge of particle arrangement, why increasing the pressure has little effect on the rate of reaction.
Question 33
2 marks · Hard
Answer and see the solution →A reaction takes place between two gases. The pressure is increased by decreasing the volume of the container.
Explain why this leads to a faster reaction rate, using ideas about particle collisions.
Question 34
2 marks · Hard
Answer and see the solution →State two features that are always true for catalysts when used in a chemical reaction.
Question 35
5 marks · Hard
Answer and see the solution →A student investigates the reaction below:
(a)[2 marks]Describe how the student could show that manganese(IV) oxide acts as a catalyst in this reaction.
(b)[2 marks]After the reaction, the student filters, dries, and reweighs the manganese(IV) oxide. The mass is unchanged. Explain why this result supports the conclusion that manganese(IV) oxide is a catalyst.
(c)[1 mark]State why only a small amount of catalyst is usually needed for a reaction.
Question 36
2 marks · Hard
Answer and see the solution →Explain why the same catalyst cannot usually be used for every type of chemical reaction.
Question 37
2 marks · Hard
Answer and see the solution →The diagram below shows a reaction profile for an exothermic reaction. The activation energy for the uncatalysed reaction is much larger than for the catalysed reaction.
Reaction profile for an exothermic reaction (uncatalysed and catalysed). Describe what the dashed line on this diagram represents. Explain how a catalyst causes this change.
Question 38
5 marks · Hard
Answer and see the solution →A student draws the following reaction profile diagram for a certain chemical reaction:
Reaction profile for a chemical reaction. Use the diagram to answer the questions below.
(a)[1 mark]State the term used for the energy difference from the reactants up to the peak without a catalyst.
(b)[2 marks]Describe how the diagram shows the effect of a catalyst on the reaction.
(c)[2 marks]Explain why many more particles in the reaction mixture can react when a catalyst is used, referring to the activation energy.
Question 39
2 marks · Hard
Answer and see the solution →A student says that using a catalyst lowers the energy of the reactants in a chemical reaction. Evaluate this statement. Use ideas from reaction profile diagrams in your answer.
Question 40
5 marks · Hard
Answer and see the solution →The diagram below shows the energy changes during a chemical reaction.
(a)[2 marks]Explain, in terms of activation energy, how a catalyst increases the rate of a reaction.
(b)[2 marks]A student suggests that adding a catalyst would change the total enthalpy change (ΔH) of a reaction. Is this correct? Explain your answer.
(c)[1 mark]Describe, using a reaction profile diagram, what happens to the activation energy and enthalpy change of a reaction when a catalyst is used.