How does enthalpy relate to internal energy?

1 Answer
Nov 3, 2015

Answer:

H = U + PV

Explanation:

H = U + PV

where H = enthalpy,
U = internal energy,
P = pressure,
and V = volume

Consider a process occurring at constant pressure and where the only work allowed is pressure-volume work (#w = -PΔV#):

The change on enthalpy is then given by:

#DeltaH=DeltaU+Delta(PV)=>DeltaH=DeltaU+PDeltaV#

and #DeltaU=q_P+w=> DeltaU=q_P-PDeltaV#

Replacing #DeltaU# by its expression in the expression of #DeltaH#
we get:

#DeltaH=q_P# at constant pressure.