Changes of state occur at particular temperatures, so the heat associated with the process is given by:

freezing or melting: Q = mL_f

where L_f is the latent heat of fusion

Boiling or condensing: Q = mL_v

where L_v is the latent heat of vaporization

For water the values are:

L_v = 2256 kJ/kg

L_f = 333 kJ/kg

c = 4.186 kJ/(kg °C)