# Change in enthalpy equal to heat transferred

1. Is the relation $\Delta H = Q _P$ valid for both reversible and irreversible processes or only for reversible processes?

$Q_P$ is the heat exchanged at constant pressure.

1. Specifically, is it valid for this case: saturated water (mass fraction = 1) is enclosed in one partition a box having two partitions of equal volume, the partition being evacuated. The partition is broken and the evacuated region gets filled with a mixture of water and steam. The temperature of the apparatus is maintained at $100^\circ\, \mathrm{C}$ (therefore the process will also be isobaric, from the phase diagram of water).