Question:
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.
Solution:
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.