Problem 9.13

[Gurvardaan Bal1L]

For problem 9.13, why is R used instead of heat capacity for the entropy equation regarding temperature change?

[Wayland Leung]

Yea i was also wondering why the heat capacity wasn't needed. Would we be wrong if we used the heat capacity?

[Nancy Dinh 2J]

For problem 9.13, why is R used instead of heat capacity for the entropy equation regarding temperature change?

Heat capacity by definition is the amount of energy required to raise the temperature of a certain amount of substance by 1 kelvin. In the problem however, you're not raising or lowering the temperature because it is at a constant 85 degrees C. Therefore, you have no use for the formula delta S = n*C* ln(T2/T1), which is what I'm guessing you were thinking of.

Instead, use delta S=n*R*ln(V2/V1). You can see how they derived this equation on page 323.

[Cali Rauk1D]

how do you know when to change it from T2/T1 to V2/V1?

[Christine Wastila 1H]

9.13 is listed in the solution manual errors page on the class website. It should be C instead of R for calculating entropy change due to a change in temperature.