Work out enthalpy change instantly with clear inputs, formula shown and shareable results.
Enthalpy is defined as H = U + PV, so at constant pressure dH = dU + P.dV. Adding 5 kJ of internal energy while expanding 0.02 m3 against atmospheric pressure costs 2027 J of expansion work, making the enthalpy change 7027 J. This is why constant-pressure heat capacities exceed constant-volume ones.
Enthalpy change
dH = dU + P dV at constant pressure
Definition
H = U + P V
Because most chemistry happens in open vessels at constant pressure, where the heat exchanged equals dH directly. It saves accounting for expansion work every time.
Only when the system expands. A reaction that contracts, such as gas-consuming combustion, has dH smaller than dU.