1. The problem statement, all variables and given/known data One mole of Ar initially at 325K undergoes an adiabatic expansion against a pressure Pexternal=0 from a Volume of 10.5L to 95.0L. Calculate the final Temperature using Ideal Gas and Van der Waals equations of state. Assume Cv,m=(3/2)R. 2. Relevant equations PV=nRT P=(RT/Vm-b) - (n2a/v2 3. The attempt at a solution I assumed Cp,m=20.8 J/mol K and Cv,m=12.47 J/mol K due to the ratios. Also since it's adiabatic q=0 Initial Volume = 10.5 L Final Volume = 95.0 L Using my professors notes for an example of a similar problem I found the equation: Tf = Ti*(Vm,i / Vm,f) gamma Gamma - Cp,m/Cv,m . So gamma = 1.4 My math was Tf=325 K * (10.5L/95L)0.4 Tf=135K My concern is I'm not sure if I won't get full credit since I didnt really use the van der waals equation of state or even the ideal gas law to my knowledge. Can anyone provide some help?