1. The problem statement, all variables and given/known data Why does a gas behave as ideal if the Isotherm and Isenthalp are parallel. 2. Relevant equations h=u+pv T1=T2, P1V1=P2V2 3. The attempt at a solution h1=u1+p1v1, h2=u2+p2v2 h2=h1 so u1+p1v1=u2+p2v2 and p1v1=p2v2 Does that mean internal energy for an ideal gas is zero? I don't understand. Thanks in advance!