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AQA GCSE · Question 03.2 · Chemical changes
Hydrogen gas reacts with oxygen gas to produce water. Water is decomposed into hydrogen gas and oxygen gas using electricity.
Which other word describes the overall process?
Hydrogen gas reacts with oxygen gas to produce water. Water is decomposed into hydrogen gas and oxygen gas using electricity.
Which other word describes the overall process?
Answer options:
A.
Alloying
B.
Combustion
C.
Corrosion
D.
Endothermic
E.
Reversible
How to approach this question
The question asks for a second word to describe the process. The prompt states that water can be made from H₂ and O₂, and also that water can be broken down into H₂ and O₂. What is the term for a reaction that can go in both directions?
Full Answer
E.Reversible✓ Correct
The correct answer is Reversible. Because water can be formed from hydrogen and oxygen, and also decomposed back into hydrogen and oxygen, the overall process is reversible.
The reaction between hydrogen and oxygen (2H₂ + O₂ → 2H₂O) is the forward reaction. The decomposition of water by electrolysis (2H₂O → 2H₂ + O₂) is the reverse reaction. Since the reaction can proceed in both directions, it is described as a reversible reaction. This is often represented by a double arrow: 2H₂(g) + O₂(g) ⇌ 2H₂O(l). The other correct term was combustion, which describes the forward reaction specifically.
Common mistakes
✗ Choosing a term that only describes one direction of the reaction.
✗ Not understanding the definition of a reversible reaction.
Practice the full AQA GCSE Chemistry Higher Tier Paper 2
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