1. The problem statement, all variables and given/known data In an adiabatic irreversible expansion of ideal gas , if Pext = 0 then which is true, A. T2=T1 B. Q=0, C. P1V1= P2V2 D. P1V1γ= P2V2γ 2. Relevant equations ΔU = Q - W For ideal gas, PV= nRT ΔU ∝ ΔT 3. The attempt at a solution I know Q= 0, Work done is zero, So ΔU = 0, hence T2= T1, So also P1V1 = P2V2, But why option D is incorrect? I now, Also have a problem that why work done is zero. Doesn't the gas will do work in expanding? Our work done will be zero.