## Cp and Cv

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

Victoria Luu - 1C
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

### Cp and Cv

When do you know to use Cp=5/2R and Cv=3/2 R for enthalpy calculations and entropy calculations?

Sydney Tay 2B
Posts: 64
Joined: Fri Sep 28, 2018 12:20 am

### Re: Cp and Cv

You only really need to know these when solving for entropy. They're used for monatomic ideal gases for the equation deltaS = n*C*ln(T2/T1). The heat capacity changes depending on if pressure or volume is held constant.

Posts: 62
Joined: Fri Sep 28, 2018 12:15 am

### Re: Cp and Cv

Cp is for when there is constant pressure whereas Cv is when there is constant volume. Hope this helps!

Nico Edgar 4L
Posts: 32
Joined: Fri Sep 28, 2018 12:19 am

### Re: Cp and Cv

Also since entropy is a state function, even if there is a volume change and a temperature change, we can still use Cv as we end up summing the two entropy changes. We assume that volume was constant over the temperature range so we can use Cv. See 4F11 in the 7th edition.