Chemical Equilibria | AQA A-Level Chemistry (7405)
Chemical Equilibria
- 80 questions
- 5 subtopics
- Physical chemistry, drawn on by Paper 1 and Paper 2
- Paper 1, Paper 2 and Paper 3
Chemical equilibria is examined on Papers 1, 2 and 3.
It covers what a dynamic equilibrium is, how Le Chatelier's principle predicts the effect of a change, why industry settles for compromise conditions, and the two equilibrium constants.
Sample questions from Chemical Equilibria
Answer each one closed book first, then open the answer.
-
Dynamic Equilibrium and Le Chatelier's Principle
What happens to the position of equilibrium when the concentration of a product is removed?
Show the answer
The position of equilibrium shifts to the right (towards products) to replace the removed product. -
Dynamic Equilibrium and Le Chatelier's Principle
How does a catalyst affect the rate at which equilibrium is reached?
Show the answer
A catalyst increases the rate at which equilibrium is reached. -
Industrial Compromise Conditions
Why is a very high pressure not always used in industrial processes even when it would favour the products?
Show the answer
Very high pressures are expensive to maintain and require stronger equipment, increasing costs. -
Industrial Compromise Conditions
What role does a catalyst play in reaching compromise conditions for an industrial equilibrium process?
Show the answer
A catalyst increases the rate of reaction, allowing equilibrium to be reached more quickly. -
The Equilibrium Constant Kc
Why do the units of Kc vary between different equilibria?
Show the answer
Because the powers to which concentrations are raised differ depending on the balanced equation -
The Equilibrium Constant Kc
Does changing pressure affect the value of Kc?
Show the answer
No, changing pressure does not change the value of Kc -
Partial Pressures and Mole Fractions
What is the relationship between partial pressure, mole fraction, and total pressure?
Show the answer
Partial pressure = mole fraction × total pressure. -
Partial Pressures and Mole Fractions
If a gas mixture contains 2 mol of gas A and 3 mol of gas B at a total pressure of 100 kPa, what is the partial pressure of gas A?
Show the answer
Mole fraction of A = 2 ÷ (2 + 3) = 0.4, so partial pressure of A = 0.4 × 100 = 40 kPa.
The 5 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Dynamic Equilibrium and Le Chatelier's Principle | The conditions for dynamic equilibrium, and predicting the effect of concentration, pressure and temperature. | 20 |
| Industrial Compromise Conditions | Why the Haber and Contact processes trade yield against rate and cost. | 15 |
| The Equilibrium Constant Kc | Writing the Kc expression, calculating it from equilibrium amounts, and working out its units. | 18 |
| Partial Pressures and Mole Fractions | Mole fraction, partial pressure, and calculating both from a gas mixture. | 9 |
| The Equilibrium Constant Kp | Writing Kp for a gaseous equilibrium, and the effect of temperature and of a catalyst on its value. | 18 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
-
Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
-
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
-
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
AQA A-Level Chemistry Active Recall Guide
Every topic, not just this one. 2,442 questions with their answers.