# Homework Help: Problem 5.15 of Statistical Physics by Reif ( Calculation of entropy)

1. Dec 23, 2012

### nuclear_dog

1. The problem statement, all variables and given/known data
1 kg of water with specific heat (C) of 4180 Joules /kg/degree is given at 0°C. It is taken to 100°C by two methods :-
(i) by bringing it in contact with a reservoir at 100°C.
(ii) by bringing it in contact with a reservoir at 50°C , and then with another reservoir at 100°C.

Calculate the entropy change of water and the reservoir in both cases.

2. Relevant equations

3. The attempt at a solution
Well, for a small amount of heat transferred (dQ), the entropy change is given by dS = $\frac{dQ}{T}$ . dQ can be calculated by the formula dQ = C*m*dT . Then ΔS is obtained by integrating between Tf and Ti . So ΔS comes out to be C*m*ln(Tf/Ti). By this method I get the same answer in both the cases.

2. Dec 23, 2012

### rude man

You have (correctly) computed the change in entropy of the water but what happened to the changes in entropy of the three reservoirs?

3. Dec 23, 2012