1. The problem statement, all variables and given/known data Consider a system consisting of 2.0 mol CO2 (assumed to be a perfect gas) at 298K confined to a cylinder of cross-section 10cm^2 at 10 atm. The gas is allowed to expand adiabatically and reversibly against a constant pressure of 1 atm. Calculate W, Q, ΔU, ΔH, and ΔT when the piston has moved 200cm. (Ans: W=-1.6KJ, Q=0, ΔU=-1.6KJ, ΔT=-28, ΔH=-2.1KJ) 2. Relevant equations The thermodynamics equations 3. The attempt at a solution as it is adiabatic, Q=0. ΔV=0.001m(0.2m)=2x10^-4 m3 W=-PexΔV=-101325(2x10^-4)=-20.27 J ΔU=W+Q=-20.27 J and i found that my W and ΔU are wrong what's wrong with my answer? should Pgas=Pex if the system is in equilibrium? i just found that it isn't but in my book : "To achieve reversible expansion we must match Pex to P at each state: dw=-Pex dV=-P dV" i am so confused. please help!