Question

Prove that water evaporation is not spontaneous in 25°C standart!

Answer 1

For a reaction to be spontaneous ΔG (Gibbs free energy) should be negative and it should releases free energy and moves to a lower.i.e.exothermic, more thermodynamically stable energy state

On the other hand Evaporation is a physical change whereby a liquid substance is changing to its gaseous form.

Evaporation will absorb heat to break the inter-molecular forces. When evaporation absorbs heat, an endothermic process has occured.

Exothermic = Release heat ( Example : Freezing water)
Endothermic = Absorb heat (Example : Evaporation of water)

Also Standard Gibbs free energy of formation of liquid water at 298 K is (-237.17 KJ/mol) and that of water vapour is (-228.57KJ/mol). Therefore,Standard Gibbs free energy of formation of H₂O(l)>H₂O(g).

Thus the water evaporation is not a spontanetous because the process is endothermic and ΔG is positive (H₂O(l)>H₂O(g)).