1. The problem statement, all variables and given/known data A solid metallic cube of heat capacity S is at temperature 300K. It is brought in contact with a reservoir at 600K. If the heat transfer takes place only between the reservoir and the cube, the entropy change of the universe after reaching the thermal equillibrium is A. 0.69S B. 0.54S C. 0.27S D. 0.19S [Answer : 0.19S] 2. Relevant equations (heat supplied)=SΔT Q = SΔT Change in entropy = (change in heat Q)/T ΔE = Q/T [I have taken entropy as E rather than usual S since S is already taken for heat capacity] 3. The attempt at a solution Should I take reservoir as an infinite pool of temperature? Then, I get Q = SΔT Q=S*(600-300) since, at thermal equillibrium the temperatures are same Q=300S ΔE=(300/600)=0.5 which is not the answer If I take reservoir which loses temperature, I am unable to continue with the problem since I do not know the heat capacity of it. Is there a different approach to this problem?