Question

Consider the evaporation of water. The standard change in the free energy is positive with ΔG∘rxn=+8.59kJmol. One might expect this process to occur in the opposite direction, with water vapor condensing into liquid water. How can the evaporation be spontaneously under normal conditions?

Answer 1

Answer:

The partial pressure of water is much less than 1atm, so the free energy change for the process must be negative with ΔGrxn<0.

Explanation:

Water vapor will condense into liquid water when the water vapor is in its standard state, with a pressure of 1atm. Under normal circumstances, the partial pressure of water vapor is much less that 1atm. It is in a nonstandard state. The free energy change of this reaction has to be negative in order to make the reaction spontaneous.