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Tiffany Cao 1D
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Joined: Fri Sep 29, 2017 7:03 am
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Postby Tiffany Cao 1D » Sun Jan 28, 2018 1:06 pm

For problem 9.13, why do we use the change in entropy=nRln(T2/T1) instead of the change in entropy=nCv(T2/T1)?

Tia Tomescu 2D
Posts: 42
Joined: Fri Sep 29, 2017 7:06 am

Re: 9.13

Postby Tia Tomescu 2D » Sun Jan 28, 2018 1:40 pm

Because pressure is increased so we can't use the second equation (Cv is at constant pressure!)

Rakhi Ratanjee 1D
Posts: 59
Joined: Fri Sep 29, 2017 7:04 am

Re: 9.13

Postby Rakhi Ratanjee 1D » Sun Jan 28, 2018 6:07 pm

Why do we have to calculate the separate entropies for change in temperature and change in volume and add them up to create the total entropy? Is there any way to combine these two changes into one equation?

Anh Nguyen 2A
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Re: 9.13

Postby Anh Nguyen 2A » Sun Jan 28, 2018 9:14 pm

I don't think we can combine those two processes in one equation because to calculate entropy change for change in temperature, we assume that the volume is constant (ΔS=n.Cv.ln(T2/T1)) and for change in volume, we assume that the temperature is constant (ΔS=n.R.ln(V2/V1)). They have to be separate in order to use the formula for each process.

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