Here's a very good question:
We all know that the enthalpy of vapourization varies with temperature, that is for a phase transition of the form A(l) to A(g), the enthalpy change ΔH will generally change with temperature. Therefore, the question in mind is: what do you think the value ΔH for vapourization is when the temperature tends towards infinity?
A good Physical chemist should have a good gut feeling! :p