How does pressure affect enthalpy?
1 Answer
Enthalpy is the heat content of a system as a function of entropy and pressure.
As the pressure increases (
= q + w + PDeltaV + VDeltaP + DeltaPDeltaV
= TDeltaS - PDeltaV + PDeltaV + VDeltaP + DeltaPDeltaV
= TDeltaS + VDeltaP + DeltaPDeltaV
Enthalpy can still exist even at constant pressure; that describes the enthalpy of vaporization or fusion.
Notice how the equation changes at constant pressure (
DeltaH = TDeltaS + cancel(VDeltaP + DeltaPDeltaV)^(0)
Thus:
(DeltaH_(vap))/(T_(vap)) = q_(rev, P)/T_(vap) = DeltaS_(vap)
(DeltaH_(fus))/(T_(fus)) = q_(rev,P)/T_(fus) = DeltaS_(fus) where
q_P is heat flow at a constant pressure.