Although heat is a path function but heats absorbed by the system under certain specific conditions is independent of path. What are those conditions? Explain.

Heat is independent of the path under 2 conditions:


1. When the volume of the system is kept constant-


By 1st law of thermodynamics:
q = ΔU + (-w)
and -w = pΔV


Therefore , q = ΔU + pΔV
ΔV = 0 (at constant volume)


Hence, qv = ΔU + 0 = ΔU= change in internal energy


2. When the pressure of the system is kept constant –


At constant pressure, qp= ΔU + pΔV


But , ΔU + pΔV = ∆H


Therefore , qp = ∆H = change in enthalpy.


1