Enthalpy
A thermodynamic state function equal to internal energy plus the product of pressure and volume.
Formula / equation
H = U + pV
Unit
kJ/mol
In depth
Enthalpy was defined so that, at constant pressure, its change equals the heat exchanged — exactly the condition of an open beaker. This makes it the natural energy quantity for chemistry, since almost all laboratory reactions occur under atmospheric pressure.
Examples in the real world
The 890 kJ/mol released when methane burns is an enthalpy change measured at constant pressure.