# What is the significance of enthalpy definition not under constant pressure?

Under constant pressure (and only PV work), change in enthalpy can be shown to equal change in heat. If enthalpy is not meaningful outside of constant pressure, then why not use heat instead? So I think it must be meaningful outside of constant pressure scenarios, but I couldn't figure it out myself. Can someone help?

• Do you know abt internal energy? Apr 21 '15 at 23:56