UPSC Combined Geo-Scientist, Mains · 2017 · Mains Paper II
Q11(b). Entropy signs for a cooling cup of tea
Question
The temperature of a hot cup of tea decreases spontaneously in a closed system at constant pressure without losing its mass. So for this change ΔS(system) < 0, ΔS(universe) > 0 and ΔS(surroundings) > 0. Justify with reasons.
Model answer
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Coverssecond law of thermodynamicsentropy of surroundingsspontaneous coolingclosed system
All parts of Question 11
- 11(a) Deriving the freezing-point depression ΔTf = Kf·m10 marks
- 11(b) Entropy signs for a cooling cup of tea10 marks