1. The problem statement, all variables and given/known data A sample of 4.00mol of oxygen is originally confined in a 20L vessel at 270K and then undergoes adiabatic expansion against a constant pressure of 600torr until the volume has tripled. Find q, W, dT, dU, dH. 2. Relevant equations U=q+w H=U+PV 3. The attempt at a solution q=0 (Adiabatic) w=-pexΔV U=w ΔT= ΔU/Cv ΔH=0 The reason I'm posting this is because I believe that all of the above is correct, but my friend claims that ΔH is not zero. First of all, ΔH=q for a constant pressure expansion, and q=0, so ΔH=0, right? Also: ΔH=ΔU+Δ(PV)=w+ PΔV= -PΔV+PΔV=0 I believe oxygen is considered a perfect gas in this question, because we are expected to calculate C(v) from C(p)-C(v)=nR So, am I right, does ΔH=0? EDIT: So, I get different answers depending on whether I use ΔH=ΔU+Δ(PV) or ΔH=ΔU+Δ(nRT) Shouldn't they be the same? shouldn't Δ(PV)=Δ(nRT) ? I've been obsessing over problems like this for weeks now. Every time I figure one thing out another thing pops up that just confuses everything for me.