Reversible reactions & equilibrium
Edexcel GCSE Chemistry revision on Reversible reactions & equilibrium. Aligned to the Pearson Edexcel GCSE Chemistry 1CH0 specification. This bank has 7 practice questions on this topic.
Sample questions (3 of 7)
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Question 1
A reversible reaction is one where...
- A) The reaction stops permanently
- B) Reactants form products AND products can re-form reactants
- C) Only one direction works
- D) All reactants become solids
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Answer: Reactants form products AND products can re-form reactants
Reversible reactions: A + B <=> C + D (note the double arrow). Example: hydrated copper sulfate <=> anhydrous + water. At EQUILIBRIUM, forward + backward reactions happen at the same rate - so concentrations stay constant (but reactions still happen). Closed systems only - if products escape, no true equilibrium.
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Question 2
At equilibrium...
- A) All reaction stops
- B) Forward + backward reactions happen at equal rate; concentrations stay constant
- C) Only reactants are present
- D) Only products are present
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Answer: Forward + backward reactions happen at equal rate; concentrations stay constant
Key concept: equilibrium is DYNAMIC, not static. Molecules constantly switching between reactant + product forms - but the rates are equal so net concentrations stay still. Position of equilibrium can be towards products (right) or reactants (left), depending on conditions.
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Question 3
Le Chatelier's principle: when conditions change, equilibrium shifts to...
- A) Oppose the change
- B) Match the change
- C) Stop the reaction
- D) Reverse forever
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Answer: Oppose the change
Le Chatelier: if you change conditions (concentration, temperature, pressure), the equilibrium shifts to OPPOSE the change. Add more reactant -> shifts right (uses it up). Remove product -> shifts right (makes more). Increase temperature on EXOTHERMIC reaction -> shifts LEFT (endothermic direction absorbs the heat). Increase pressure on a gas reaction -> shifts to fewer gas molecules.
Want to test yourself on the remaining cards for this topic?
4 more questions on Reversible reactions & equilibrium — plus mistakes tracking and spaced repetition across the whole Chemistry spec.