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Enthalpy

Equation (4.13) shows a very restricted case where the heat transfer during the process is given in terms of the change in the quantity (U + PV) between the state 1 and 2. Each term of (U + PV) is the property of a substance that is a function of the state of the system, their combination must also be a property. We term this property as enthalpy. So

H (enthalpy)= U + PV

H/M = U/m + PV/m

h = u + Pv

h = specific enthalpy; the S.I. unit of h is J /kg.

dq = du + dw

= du + Pdv

=du + d(Pv)

= d (u + Pv)

= dh.