Question

Show that the heat absorbed at constant pressure is equal to the change in enthalpy of the system.

Answer 1

Heat absorbed at constant pressure, Q_P = Δ U + P_ext Δ V

Enthalpy, H = U + PV. Change in enthalpy at constant pressure is given by Δ H = Δ U + P Δ V

If inside pressure (P) and outside pressure P_ext are the same, Q_P = Δ U + P Δ V = Δ H.