Reversible reactions — AQA GCSE Chemistry
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Reversible reactions explained
A reversible reaction is one in which the products can react to reform the original reactants.
Read the full explanation
It is represented with a reversible arrow, so A + B ⇌ C + D shows both the forward and reverse reactions. The direction can be changed by changing the conditions. For example, heating hydrated copper(II) sulfate drives off water to form anhydrous copper(II) sulfate, and adding water reverses the change. In the Haber process, changing temperature or pressure shifts the direction in which the reaction proceeds. The reversible arrow shows that both reactions can occur, and the conditions determine which direction is favoured.
Your focus
- Define a reversible reaction and represent it using a reversible arrow.
- Describe how changing conditions can change the direction of a reversible reaction.
- Apply the idea of reversibility to examples such as hydrated copper(II) sulfate and the Haber process.
Reversible reactions exam tips
Marking Points
- A reversible reaction is one in which the products can react to produce the original reactants.
- Reversible reactions are represented using a reversible arrow, for example A + B ⇌ C + D.
- The direction of a reversible reaction can be changed by changing the conditions.
- Changing temperature, pressure or concentration can favour the forward or reverse reaction.
- Examples include the hydration and dehydration of copper(II) sulfate and the Haber process.
- The reversible arrow indicates that both the forward and reverse reactions can occur.
Examiner Tips
- 💡Write the reversible arrow clearly and correctly in equations for reversible reactions.
- 💡When explaining a change in direction, name the condition changed and state which direction is favoured.
- 💡Use a familiar example, such as hydrated copper(II) sulfate, to illustrate reversibility.
Common Mistakes
- Using a single arrow instead of a reversible arrow for a reversible reaction; the correction is to use the reversible arrow ⇌.
- Thinking the reaction stops when equilibrium is reached; the correction is that both forward and reverse reactions continue.
- Assuming the direction cannot be changed; the correction is that changing conditions such as temperature or pressure can change the direction favoured.