# Thermodynamics: entropy

1. Nov 2, 2007

### Bill Foster

1. The problem statement, all variables and given/known data

Heat leaks out of a house at the rate of $$2.5\times{10^4} \frac{kcal}{h}$$. The temperature inside the house is 21°C and the temperature outside the house is -5°C. At what rate does this process produce entropy.

2. Relevant equations

$$S(A)-S(A_0)=-\frac{\Delta{Q}}{T_1}+\frac{\Delta{Q}}{T_2}=\Delta{Q}\times{(\frac{1}{T_2}-\frac{1}{T_1})}$$

3. The attempt at a solution

Heat flows from the high temp res to the low temp res at a rate of $$2.5\times{10^4} \frac{kcal}{h} = 6944.4 \frac{cal}{s} = \Delta{Q}$$.

$$T_1=21°C=294.15K$$
$$T_1=-5°C=268.15K$$

Plugging and chugging I get: $$2.29 \frac{cal}{K\times{s}}$$, which is wrong.

The answer in the back of the book is $$8.2\times{10^3}\frac{cal}{K\times{s}}$$.

2. Nov 3, 2007