A chemist traces the warming of a 1.00 mol sample of pure water that starts as ice at −20∘C and ends as steam at 120∘C, all at 1 atm pressure. The chemist divides the overall change into the six macroscopic segments below.
Segment 1 Warm the ice from −20∘C to 0∘C
Segment 2 Melt the ice at 0∘C
Segment 3 Warm the liquid water from 0∘C to 100∘C
Segment 4 Boil the liquid at 100∘C
Segment 5 Warm the steam from 100∘C to 120∘C
Segment 6 Expand the steam isothermally at 120∘C from its initial 1 atm to a final 0.80 atm
The chemist is interested in how matter and energy dispersal evolve across the sequence.
(a) For each segment, state whether the entropy change for the water sample is positive, negative, or approximately zero. Briefly justify each choice using particulate-level reasoning.
(b) Rank the six segments from greatest to least positive contribution to the sample’s entropy change. Provide a short explanation for your ordering.
(c) Identify the single segment that most strongly depends on external pressure. Explain why a change in pressure would have a larger impact here than in the other segments.
(d) Suppose the expansion in Segment 6 were carried out to 0.50 atm instead of 0.80 atm while all other steps remained the same. Describe qualitatively how the overall entropy change for the sample would be altered and justify your prediction.