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A solid body of constant heat capacity 1 J/°C is being heated by keeping it in contact with reservoirs in two ways: (i) Sequentially keeping in contact with 2 reservoirs such that each reservoir supplies same amount of heat. (ii) Sequentially keeping in contact with 8 reservoirs such that each reservoir supplies same amount of heat. In both the cases body is brought from initial temperature 100°C to final temperature 200°C. Entropy change of the body in the two cases is:

1. ln2, 2ln2
2. 2ln2, 8ln2
3. ln2, 4ln2
4. ln2, ln2

Correct answer: ln2, ln2

Solution

Entropy change of the body depends only on its initial and final temperatures (a state function), so it is identical regardless of the number of reservoirs: dS = C*ln(Tf/Ti) = ln2 in both cases.

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