# Calculate latent heat

1. Jan 3, 2009

### KFC

We could use the change of entropy before and after eh phase changed to calculate the latent heat

$$L = (S_{after} - S_{before})T$$

and in some case, if we know the relation of pressure and temperature, we can also apply Clausius-Clapeyron relation to calculate the latent heat.

I wonder if there is any usual way to calculate the latent heat for phase change. If the pressure is unchanged we see that then change of enthalpy is same the

$$\Delta H= T\Delta S$$

So can I say the latent heat of phase change b/w any two phase for any system is equal to the change of enthalpy of this system during the phase change?

Last edited: Jan 3, 2009
2. Jan 4, 2009

### olgranpappy

Yes, it's okay since the transition occurs at constant temperature and pressure.

$$L\equiv\Delta Q = T\Delta S=\Delta H - V\Delta P=\Delta H\;.$$