## Change in entropy when temperature changes

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Drishti_Jain_1D
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### Change in entropy when temperature changes

For some textbook problems, the change in entropy when temperature changes uses the equation S=nCln(T2/T1) and for some, the equation S=nRln(T2/T1) is used. How do you know which equation to use under certain conditions?

Chem_Mod
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### Re: Change in entropy when temperature changes

This comes from $\Delta S= \frac{q_{rev}}{T}$, when does q equal $nC\Delta T$, and when does q equal $nR\Delta T$? The first one is when you are calculating the q (and subsequently entropy) of a substance with a specific heat of C (needs to be defined with const. V or P). And then the second one is used in work calculations (for an ideal gas).

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