Two identical metal blocks are placed in thermal contact inside an insulated container
PHYSICS · Single correct · AP · Physics 2: Algebra-based · Thermodynamics · Thermodynamics
Problem
Two identical metal blocks are placed in thermal contact inside an insulated container. Block X is initially at 350 K, and block Y is at 300 K. After a long time they reach a common temperature.
Which of the following best explains why the total entropy of the two-block system increases even though block X experiences a decrease in entropy?
(a) Because the container is insulated (adiabatic), no heat is exchanged with the surroundings, so the total entropy of the two blocks must remain constant.
(b) Since heat lost by X equals heat gained by Y, using ΔS=Q/Tf for both blocks gives equal and opposite entropy changes, yielding ΔStotal=0.},{
(c) Block Y’s entropy increase outweighs block X’s entropy decrease because entropy change depends on the ratio of temperatures, and the heat absorbed by the cooler block occurs at a lower average temperature.
(d) The temperature change for each block is 25K, so their entropy changes are equal in magnitude and cancel, making the total entropy zero.