1. The problem statement, all variables and given/known data There exists a tank filled with air with a given volume, temperature, and pressure. The tank exists in a room at a given temperature and pressure. That is: For the tank: P=1MPa, T=700k, V=1m^3 Outside: T=295K, P=100kPa 2. Relevant Equations \psi 2-\psi 1=(1-T0/Tb)*1Q2-[W=P0*(V2-V1)-T0*δ E2-E1=Q-W PV=mRT 3. Attempt at solution Will the transfer happen slowly enough that it is safe to assume zero reversabilities? Meaning sigma is zero? In this case I am a little confused between the definitions of internal and external reversibilities. With the assumptions that work and entropy production are zero. \psi 2-\psi 1=(1-T0/Tb)*1Q2 Then we can get Q from first law with the assumption that the tank will eventually reach the environmental temperatures. So we can get u2 and u1 from the tables at the tank conditions and the environment conditions. U2-U1=Q m(u2-u1)=Q Q/m=u2-u1 (210.49-512.33)Kj/kg*k=-301.84 Kj/kg*k=Q/m So (multiplying (Q/m)*m) m=PV/RT=171.823kg \psi2-\psi1=(1-700k/295k)*(-301.84 Kj/kg*k)*(171.823) =71,201.8302 Kj*K That is a very large number. Is that correct?