A vertical cylinder closed at both ends is fitted with a smooth piston dividing the volume into two parts each containing one mole of air. At the equilibrium temperature of 320 K, the upper and lower parts are in the ratio 4 : 1. The ratio will become 3 : 1 at a temperature of

p2-p1A=mgor                       mgA=RTiV1-RTi4V1=3RTi4V1                       …(i)Similarly, in second case,                          mgA=RTfV2-RTf3V2=2RTf3V2                       …(ii)Further, 5V1 = 4V2Equating Eqs. (i) and (ii), we get                        3Ti4V1=2Tf3V2⇒                        Tf=98×V2V1×Ti                                  = 98 × 54 × 320                                   = 450 K