The relation between enthalpy change and internal energy change is
ΔH = ΔU + PΔV
Explanation:
The state function Enthalpy, denoted as H, was introduced as most of the chemical reactions were performed at constant pressure.
Enthalpy is the thermodynamic equivalent to the net heat content of the system.
In accordance, with the first law of thermodynamics:
The enthalpy of the system is the sum of the internal energy and the pressure-volume change.
It is a state function.
Hence, ΔH = ΔU + PΔV.