Chemical Equilibrium and Reaction Rate: Reversible Reactions, Le Chatelier's Principle and the Five Rate Factors

Chemical Equilibrium and Reaction Rate: Why Some Reactions Stop Halfway

Burn a piece of paper and it never turns back into paper. Yet when nitrogen and hydrogen react to make ammonia, ammonia also breaks back into nitrogen and hydrogen in the same vessel. Two questions follow. How far does a reaction go before it seems to stop? That is equilibrium. How fast does it get there? That is rate.

The two ideas are different, and exams love to mix them up. A catalyst changes how fast equilibrium is reached but not where it settles. Heating speeds up every reaction but can push the equilibrium either way.

This short covers reversible and irreversible reactions, dynamic equilibrium, Le Chatelier's principle with the Haber process as the running example, and the factors that control rate. The industrial plants themselves belong to the catalysts topic; here the focus is the reasoning.

1. Which statement about dynamic chemical equilibrium is correct?

2. For N2 + 3H2 ⇌ 2NH3, what happens when the pressure is increased?

3. What is the role of the iron catalyst in the Haber process?

4. For which equilibrium will a change in pressure have no effect?

5. Why does powdered chalk react with dilute hydrochloric acid faster than a lump of chalk of the same mass?

6. The forward reaction in ammonia synthesis is exothermic. What does raising the temperature do to the equilibrium yield of ammonia?

7. Which of the following is an irreversible reaction under ordinary conditions?

8. Zinc granules react with dilute hydrochloric acid. Which change will NOT increase the rate of this reaction?