Chemical Equilibrium | OCR A-Level Chemistry A (H432)
Chemical Equilibrium
- 36 questions
- 4 subtopics
- Module 3: Periodic table and energy
- Component 01 and Component 03
Dynamic equilibrium and how it responds to a change: le Chatelier's principle, the compromise conditions industry actually uses, and the equilibrium constant Kc as a measure of how far a reaction goes..
It covers dynamic equilibrium and le Chatelier's principle, pressure, catalysts and investigating a shift in equilibrium, industrial compromise and the Haber process and the equilibrium constant, Kc.
Sample questions from Chemical Equilibrium
Answer each one closed book first, then open the answer.
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Dynamic equilibrium and le Chatelier's principle
Why must a system be closed for dynamic equilibrium to be established?
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No substances can enter or leave a closed system, so the reactants and products remain within the system to maintain equilibrium. -
Dynamic equilibrium and le Chatelier's principle
How does removing a product from an equilibrium mixture affect the position of equilibrium?
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The equilibrium position shifts towards the products to replace the removed product. -
Pressure, catalysts and investigating a shift in equilibrium
For the equilibrium H₂(g) + I₂(g) ⇌ 2HI(g), what effect does changing pressure have on the position of equilibrium?
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No effect, because both sides have equal moles of gas (2 moles on each side). -
Pressure, catalysts and investigating a shift in equilibrium
What is the effect of a catalyst on the time taken to reach equilibrium and on the equilibrium concentrations?
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A catalyst allows equilibrium to be reached more quickly but does not alter the equilibrium concentrations. -
Industrial compromise and the Haber process
How does equilibrium yield influence the choice of industrial conditions?
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Conditions are chosen to maximise the proportion of products at equilibrium while balancing other factors. -
Industrial compromise and the Haber process
What temperature is typically used in the Haber process and why is this a compromise?
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Around 450°C is used as a compromise between achieving a reasonable reaction rate and maintaining an acceptable equilibrium yield. -
The equilibrium constant, Kc
If a reaction has a small value of Kc, what does this tell you about the equilibrium mixture?
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The equilibrium position lies to the left, favouring reactants. -
The equilibrium constant, Kc
Why does a very large Kc indicate that almost all reactants have been converted to products?
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Because a large Kc means the ratio of product concentrations to reactant concentrations is very high, indicating the equilibrium lies far to the right.
The 4 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Dynamic equilibrium and le Chatelier's principle | Recall questions on the two conditions for dynamic equilibrium, why a closed system is needed, and the statement of le Chatelier's principle applied to concentration and temperature. | 10 |
| Pressure, catalysts and investigating a shift in equilibrium | Recall questions on the effect of pressure in a gaseous system, why a catalyst does not move the position, and how a shift can be investigated experimentally. | 8 |
| Industrial compromise and the Haber process | Recall questions on why yield, rate, safety and cost pull against each other, and on the temperature, pressure and catalyst chosen for the Haber process. | 10 |
| The equilibrium constant, Kc | Recall questions on where products and reactants sit in the Kc expression, and what a value much greater than, close to, or much less than 1 tells you. | 8 |
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.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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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.
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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 sections
OCR A-Level Chemistry A Active Recall Guide
Every section, not just this one. 1,913 questions with their answers.