1. The problem statement, all variables and given/known data An ideal gas expands isothermally in contact with a heat source. ∆U is zero in this case because it is an ideal gas and T=constant. Is this against Kelvin-Planck statement? 2. Relevant equations pv=nRT dW=-pdV Kelvin-Planck statement: There is no proccess whose only result is the full transformation of heat into work. 3. The attempt at a solution My guess is, ∆U=Q+W=0, therefore Q=integral(pdv)=nRTlog(Vfinal/Vinitial)>0 W=-nRTlog(Vfinal/Vinitial) So all the heat that the gas absorbs turns into work. Therefore, this is against K-P statement, but I have a feeling that I am wrong. Can you guys help me?