Entropy And The Second Law Of Thermodynamics

Which statement best describes the second law of thermodynamics?

A student writes: “Entropy measures how messy or disordered a system is.” Suggest the most accurate revision of this statement for an AP Physics exam.

A sealed, insulated box contains gas molecules all confined to the left half by a removable partition. The partition is removed. Predict what happens to the entropy of the gas and justify the direction of the process.

Entropy is a state function. Which consequence follows directly from this property?

A hot block of iron is placed in contact with a cold block of copper inside a sealed, perfectly insulated container. Determine what happens as the system approaches thermodynamic equilibrium.

At thermodynamic equilibrium in an isolated system, which statement about entropy is correct?

A refrigerator removes thermal energy from the food inside, lowering the temperature of the food. A student claims this violates the second law because the entropy of the food decreases. Indicate whether this claim is correct and justify your reasoning.

An engineer designs a system in which a compressed gas in one chamber does work by expanding against a piston. After the gas has expanded freely to fill the entire available volume, the engineer wants the gas to spontaneously recompress to its original volume to repeat the cycle. Using entropy concepts, explain why this design fails.

Two identical containers hold the same amount of the same gas at the same temperature and volume. Container X was filled by slow isothermal compression, and Container Y was filled by rapid adiabatic compression followed by cooling. Compare their entropies.

Which of the following scenarios correctly illustrates a process in which the entropy of a system decreases while the second law is still satisfied?

Consider the following process: a drop of ink is placed in a glass of water and gradually spreads uniformly throughout. A student claims that if you could perfectly reverse the motion of every water and ink molecule, the ink would spontaneously reconcentrate into a single drop. Using the second law, evaluate whether this reconcentration would occur in practice.

A closed system undergoes a process in which energy is transferred into the system as heat from the surroundings. Determine how the entropy of the system and the entropy of the surroundings each change, and whether the second law is satisfied.

An isolated system contains two gases separated by a partition at different pressures. The partition is removed. Which statement correctly describes the entropy change and the final state?

A well-insulated thermos contains hot coffee. Over several hours, the coffee cools slightly because the insulation is imperfect. Determine whether this thermos approximates an isolated system or a closed system, and predict the entropy change of the coffee.