A 50 g ice cube at 0 °C is dropped into a rigid, sealed container that initially contains 200 g of liquid water at 20 °C. The container is perfectly insulating and impermeable to matter. After a long time an equilibrium state is reached at 0 °C consisting of a mixture of ice and liquid water.
Answer the following, using qualitative reasoning only.
(a) Treat the liquid water alone (excluding ice) as the system. State the system type and predict the sign of its entropy change during the approach to equilibrium. Provide justification.
(b) Now treat the combination of ice + liquid water as the system. Classify the system and predict the sign of its entropy change. Explain your reasoning.
(c) Finally, redefine the system to include the insulated container and all contents (ice + water + trapped air). What type of system is this? State and justify the sign of its entropy change for the entire process.
(d) Using your answers above, discuss how different boundary choices can lead to opposite conclusions about whether entropy increases or decreases for a given subsystem, yet still remain fully consistent with the second law of thermodynamics.