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AP EAMCET2013ChemistryThermodynamics (C)

For which one of the following reactions, the entropy change is positive?

Options

  1. AH ₂(g)+ 1 2 O ₂(g) H ₂ O (l)
  2. BNa ⁺(g)+ Cl ⁻(g) NaCl (s)
  3. CNaCl (I) NaCl ( s )
  4. DH ₂ O (l) H ₂ O ( g )

Correct answer

D. H ₂ O (l) H ₂ O ( g )

Step-by-step solution

Evaporation of water in an open vessel is a process which takes place by itself, by absorption of heat from the surroundings, because the gaseous water molecules are more random than the liquid water molecules. H ₂ O (l) H ₂ O (g) ; H=+40.8 ~kJ ~mol ⁻¹ In other words, the process is spontaneous because it is accompanied by increase of entropy, which is further a measure of randomness or disorder of the system.

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