At 250C, 1 mole of butane is heated to form CO2 and H2O liquid. The work done for the given process is

W = P∆V = ∆ngRTC4H10(g) + 6.5 O2(g) →4CO2(g) + 5H2O(l)∆ng = 4 - 7.5 = - 3.5W = - 3.5 ×0.0821×298 = 85.6 L atm