Topic: Second law, entropy and spontaneity· Chemical Thermodynamics

In which case change in entropy is negative ?

1. Evaporation of water

2. Expansion of a gas at constant temperature

3. Sublimation of solid to gas

4. 2H(g) \(\to\) H\(_2\)(g)

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Answer: 4. 2H(g) \(\to\) H\(_2\)(g)

Entropy measures disorder. Evaporation, sublimation and isothermal expansion all increase randomness (\(\Delta S>0\)). In \(\mathrm{2H(g) \to H_2(g)}\) two particles combine into one, so disorder decreases and \(\Delta S<0\). Option (4).

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In which case change in entropy is negative ?

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