# Why specific latent heat of vaporisation > fusion?

1. May 12, 2016

### Janiceleong26

1. The problem statement, all variables and given/known data

2. Relevant equations
First law of thermodynamics, ΔU=q+W

3. The attempt at a solution
Ok so, I know that when liquid evaporates, the change in volume is much greater than that when solid melts. And for both cases, distance of separation of atoms increases too, so PE increases, and hence, internal energy increases.
So, ΔU=mL+ pΔV
L=(ΔU-pΔV) /m
But how do we know that the term (ΔU-pΔV) is greater for vaporisation than that of fusion?

2. May 12, 2016

### Fightfish

Well, that is in fact the main essence of the answer.

There is a sign problem here. The work done on the system $W$ should be $- p \Delta V$ - do you see why?

3. May 12, 2016

### Janiceleong26

Ahh I see why now. Yup, because it's work done by system.
Thanks !