Question:
In which one of the following reactions, entropy decreases?
In which one of the following reactions, entropy decreases?
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Entropy decreases when disorder decreases. Freezing or crystallization generally causes a decrease in entropy.
Updated On: Apr 29, 2026
- Sodium chloride is dissolved in water
- Water is heated from 303 K to 353 K
- Sodium bicarbonate is decomposed to \(Na_2CO_3(s), CO_2(g)\) and \(H_2O(g)\)
- Water crystallizes into ice
- Dihydrogen molecule is decomposed into hydrogen atoms
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The Correct Option is D
Solution and Explanation
Concept:
Entropy is the measure of randomness or disorder. Entropy decreases when a system becomes more ordered.
Step 1: Compare liquid and solid states.
Liquid water has more randomness than ice because molecules can move more freely.
Step 2: During crystallization.
When water crystallizes into ice: \[ \text{Liquid} \rightarrow \text{Solid} \] The molecules become more ordered.
Step 3: Conclusion.
Since order increases, randomness decreases. Therefore, entropy decreases.
Step 1: Compare liquid and solid states.
Liquid water has more randomness than ice because molecules can move more freely.
Step 2: During crystallization.
When water crystallizes into ice: \[ \text{Liquid} \rightarrow \text{Solid} \] The molecules become more ordered.
Step 3: Conclusion.
Since order increases, randomness decreases. Therefore, entropy decreases.
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