Why enthalpy changes in phase transition when there is no change of temperature?

Why there is a change in enthalpy in phase transition?

I'm asking because enthalpy depends only on temperature:

$$\mathrm dH = C_p\,\mathrm dT,$$

and the change in temperature is $$\mathrm dT = 0.$$

• It depends on n, P, V. too. dH = Q isn't general as in your statement. Your book or notes should have all. – Alchimista Jul 16 at 10:14

For a single phase, enthalpy is a function of temperature and pressure, and, at constant pressure, $$\mathrm dH = C_p\,\mathrm dT.$$