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## Homework Statement

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)

## Homework Equations

The thermodynamics equations

## 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!