C. Adiabatic irreversible expansion against a constant pressure of Pz. J/K Your answer: AS = d. Adiabatic reversible expansion. Your answer: AS = J/K 1. You have one mole of a monatomic ideal gas at the initial volume V1 = 2 L and initial temperature Ti = 500 K. Calculate the change in entropy for the following types of expansion to the final volume V2 = 6 L. Irreversible expansion against a constant (and final) pressure of P2 = P2/2. a. Your answer: AS = J/K b. Irreversible expansion against a vacuum (free expansion). Your answer: AS = J/K