## conceptual question about change in entropy due to both temp and vol [ENDORSED]

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

Annie Lieu-1H
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### conceptual question about change in entropy due to both temp and vol

I understand that it's a 2 step process that we end up adding all together. But why do we use constant volume for the temperature equation? The volume is changing, so how is it heat capacity at constant volume?

Janet Nguyen 2H
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### Re: conceptual question about change in entropy due to both temp and vol

We are assuming, by using the two step process, that first the volume increases and then the temperature increases(or decreases whatever the problem says) so when the temperature is changing, the volume has already changed and is now constant

Chem_Mod
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### Re: conceptual question about change in entropy due to both temp and vol  [ENDORSED]

The change occurs in one step with both volume and temperature changing at the same time.
But since entropy is a state function we can separate it into two steps to make the calculation possible for each step, and then add them.

The overall process is separated into two steps to make the individual calculations easier:

1: Decreased the volume, keep temperature constant.

2: Increase the temperature, keep volume constant.

I will likely discuss this in class during my review as many students have asked this.

Make sure to discuss it in the Workshops, Step-Up Sessions, Discussion Sections, Office Hours, and Reveiw Sessions.

Jessica Lutz 2E
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### Re: conceptual question about change in entropy due to both temp and vol

Is there a reason you do it in that order? Or would you get the same answer if you changed the temperature first with a constant volume?