# Enthalpy is a State Function


Our expression for internal energy at constant pressure:

$\Delta U=q_P+w=q_P-P\Delta V \nonumber$

Rearrange:

$q_P=\Delta U+P\Delta V=U_2-U_1+P(V_2-V_1) \nonumber$ $q_P=\left(U_2+PV_2\right)-\left(U_1+PV_1\right) \nonumber$

We can define this term as enthalpy:

$H\equiv U+PV \nonumber$

This is a new state function.

Enthalpy is a State Function is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.