(A) Change in internal energy is expressed asΔU=nCvΔT, here, ΔT is change in temperature.
Since, in an isothermal process temperature remains constant, thus, ΔU=0
A→II
(B) In an adiabatic process, heat transfer, Q=0.
So, from first law of thermodynamics,
Q=ΔU+W
ΔU=−W
Since, work done by gas is positive, thus, ΔU is negative
B→I
(C) In an isochoric process, volume remains constant, so work done by or on the gas W=PΔV=0
C→IV
(D) In an isobaric process, pressure remains constant, so work doneW=PΔV=0 and change in internal energy ΔU=nCvΔT=0
Thus, heat absorbed goes partly to increase internal energy and partly do work.
D→III