enthalpy   Symbol H. The thermodynamic variable enthalpy is defined as,

H = U + pV

where U is the internal energy. The infinitesimal change in the enthalpy is,

dH = (dU + pdv) + Vdp

= dQ + Vdp

using the first law of thermodynamics.

During isobaric process dp = 0, Therefore,

dH = dQ

or H_f - H_i = CpdT

The  enthalpy function is more useful to engineers and chemists because isobaric processes are important in these branches.