In thermodynamics and molecular chemistry, the enthalpy (denoted as H, or specific enthalpy denoted as h)'s a thermodynamic property of a fluid. It can be used to calculate the heat transfer during a quasistatic process taking place in a closed thermodynamic system under constant pressure. Enthalpy H's an arbitrary concept but the enthalpy change ΔH's more useful because it's equal to the change in the internal energy of the system, plus the work that the system has done on its surrounding… (More on Enthalpy)