Calculating Entropy with Change in Temperature

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

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Semi Yoon
Posts: 60
Joined: Fri Sep 28, 2018 12:27 am

Calculating Entropy with Change in Temperature

Calculate the change in entropy when the pressure of 5.75g of helium gas is decreased from 320kPa to 40kPa while the temperature decreases from 423K to 273K. Assume idea behavior.

I know that you should use two equations: deltaS=nRln(P1/P2) and deltaS=nCvln(T2/T1).

Why would you use Cv and how would you find it in the second equation? After finding deltaS for both equations, do you add the two values together or subtract them?

Alana Sur 3B
Posts: 61
Joined: Fri Sep 28, 2018 12:25 am

Re: Calculating Entropy with Change in Temperature

we use Cv to calculate the heat capacity of an ideal gas with constant volume. You add the two delta S values

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