MEDIUMMCQ SINGLEJEE Mains ChemistryPhysical ChemistryThermodynamics and ThermochemistryIntroduction to Thermodynamics

In which case change in entropy is negative?

A.Expansion of a gas at constant temperature

B.Sublimation of solid to gas

C.2H(g) → H₂(g)✓ Correct

D.Evaporation of water

Explanation

The explanation of given statements are: (a) Entropy is positive in case of expansion of a gas at constant temperature. It is because during expansion of gas, volume increases and hence randomness increases. (b) Entropy is positive in case of sublimation of solid to gas as gas is much disordered than a solid. THERMODYNAMICS AND THERMOCHEMISTRY 35 (c) Entropy is negative in case of 2H(g) → H₂(g) as the number of moles of gaseous reactants are more than that of gaseous products. (d) Entropy is positive in case of evaporation of water as gas is much disordered than a liquid. Hence, option (c) is

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