1. The problem statement, all variables and given/known data Taken from adkins Introduction to thermal physics A reversible heat engine is operated between two bodies, one of heat capacity C1 initially at temperature T1 and the other of heat capacity C2 initially at temperature T2. As the engine operates, the warmer body gradually cools and the cooler one is warmed. (a) By considering the changes that occur in one cycle of the engine, show that infinitesimal changes of temperature of the two bodies are related by 0 = C1 dT1/T1 + C2 dT2/T2 Eventually, the bodies reach the same temperature Tf and the heat engine ceases to run. Show that Tf is given by TfC1 + C2 = T1C1 T2C2 2. Relevant equations U = Q + W 3. The attempt at a solution For the first part I am taking the U to be 0 and W = 0 ... This probaly is not be correct. 0 = C1 (T1 + dt) + C2(T2-dt)... this does lead me to the correct solution. Any hints would be greatly appreciated!