1. The problem statement, all variables and given/known data A piston/cylinder contains helium at 500 K and 1200 kPa. It expands polytropically with n=1.667 to a pressure of 100 kPa. Find the final temperature, the specific work and specific heat transfer in the process 2. Relevant equations U2-U1=1Q2-1W2 1W2=P2V2-P1V1/(1-n) P1*V1^n=P2*V2^n PV=mRT 3. The attempt at a solution (P1V1/T1)=mR=(P2V2/T2) I'm trying to plug that into this equation (P1*V1^n=P2*V2^n) to find P or T but I can't since I don't have enough data to use it. I only have intensive information to work with. Can I assume that this is an ideal gas or should I look for the stage it is in? What am I doing wrong?