Physical Chemistry
7 marks · EasyCatalysts are widely used in industry to speed up chemical reactions. Some industrial reactions are also reversible and take place in sealed containers.
State one reason why catalysts are important in industrial chemical reactions.
Copper(II) sulfate can be used in a reversible reaction in a sealed test tube: What is meant by a 'sealed container' in the context of a reversible reaction? (Give one feature of a sealed container relevant to the reaction above.)
Ammonia is produced by reacting nitrogen and hydrogen using an iron catalyst, in a sealed reactor. Explain how using a catalyst benefits the ammonia production process, apart from cost.
Describe how you could show experimentally that a catalyst is not used up in a reaction.
Give one feature of a sealed container that makes it suitable for studying reversible reactions.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Catalysts increase the rate of reaction, allowing reactions to proceed faster or at lower temperatures.
(b) A sealed container prevents substances (reactants and products) from escaping during the reaction.
(c) A catalyst speeds up both the forward and reverse reactions equally, so ammonia is produced more quickly, allowing the plant to operate efficiently. This increases the rate at which equilibrium is reached, even though the yield doesn't change.
(d) You could weigh the catalyst before the reaction and again after, or separate it (e.g., by filtration), dry it, and show that its mass and appearance are unchanged, demonstrating it was not used up.
(e) It stops gases or liquids from entering or leaving, so all substances remain inside the system.
Common mistakes: Saying catalysts affect yield rather than only rate; Not linking sealed container to prevention of loss of reactants/products
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States one correct reason, e.g. 'Catalysts lower energy costs by allowing lower temperatures', or 'increase rate of reaction'.
B1 (b) · 1 mark · States one correct feature: a sealed container prevents substances entering or escaping.
M1 (c) · 1 mark · Refers to the catalyst speeding up the reaction / both forward and backward reactions.
A1 (c) · 1 mark · Mentions that the catalyst allows the system to reach equilibrium faster or makes production more efficient.
M1 (d) · 1 mark · Suggests an experimental method (e.g. weighing, separating, filtering the catalyst before and after reaction).
A1 (d) · 1 mark · States result shows the catalyst is chemically unchanged (mass or appearance unchanged).
B1 (e) · 1 mark · States a feature making sealed containers suitable for reversible reactions (prevents entry/escape of substances).
Worked solution
a. Catalysts are important because they speed up reactions, allowing industrial processes to be carried out faster and often at lower temperatures, saving energy and costs.
b. In a reversible reaction, a sealed container is one that prevents substances from entering or leaving, so all reactants and products remain inside.
c. Using a catalyst in the ammonia process increases the speed at which ammonia is made by increasing the rate of both the forward and reverse reactions. Although it does not change the yield, it allows the process to operate more efficiently because equilibrium is reached more quickly.
d. To show a catalyst is not used up, weigh the catalyst before the reaction, then, after the reaction, separate it (e.g., by filtration), dry it, and reweigh it. The mass should be the same, showing it was not chemically changed or used up.
e. A sealed container prevents substances from escaping or entering, so the number of particles remains constant, letting equilibrium be established and studied.