Question:
Which of the following processes is an example of decrease in entropy?
Which of the following processes is an example of decrease in entropy?
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Entropy falls when gas molecules combine to give a liquid, since the system becomes more ordered.
Updated On: Nov 12, 2026
- Dissolution of solid iodine in water
- Formation of liquid water from hydrogen and oxygen gas
- Dissociation of hydrogen molecules into atoms
- Decomposition of calcium carbonate on heating
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept
Entropy measures disorder. It falls when the system becomes more ordered, for example when gas changes to liquid or the number of gas molecules goes down.
Step 2: Check the options
Iodine dissolving, hydrogen molecules splitting into atoms, and \(\text{CaCO}_3\) decomposing to release \(\text{CO}_2\) gas all increase disorder.
Step 3: Conclusion
In \(2\text{H}_2(g) + \text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(l)\), three moles of gas become two moles of liquid, so entropy decreases.
Final Answer:
Formation of liquid water from hydrogen and oxygen gases shows a decrease in entropy. \[ \boxed{\text{(B) }\text{Formation of liquid water from hydrogen and oxygen gas}} \]
Entropy measures disorder. It falls when the system becomes more ordered, for example when gas changes to liquid or the number of gas molecules goes down.
Step 2: Check the options
Iodine dissolving, hydrogen molecules splitting into atoms, and \(\text{CaCO}_3\) decomposing to release \(\text{CO}_2\) gas all increase disorder.
Step 3: Conclusion
In \(2\text{H}_2(g) + \text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(l)\), three moles of gas become two moles of liquid, so entropy decreases.
Final Answer:
Formation of liquid water from hydrogen and oxygen gases shows a decrease in entropy. \[ \boxed{\text{(B) }\text{Formation of liquid water from hydrogen and oxygen gas}} \]
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