## Delta S equations

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

Katherine Grillo 1B
Posts: 69
Joined: Fri Sep 28, 2018 12:28 am

### Delta S equations

I'm confused about the different delta S equations. When does delta S equal q/t vs nRln(V2/V1) vs nCln(T2/T1)?

MaanasO 1A
Posts: 72
Joined: Fri Sep 28, 2018 12:26 am

### Re: Delta S equations

Hi Katherine!

dS = q/t when you're dealing with a reversible process. dS = nRln(Vf/Vi) when the process is isothermal. dS = nCln(Tf/Ti) when there's a change in temperature associated with the change in entropy. Your C value will change based on whether your volume (Cv) or pressure (Cp) are constant.

Hope that helps!

705192887
Posts: 77
Joined: Fri Sep 28, 2018 12:18 am

### Re: Delta S equations

MaanasO 1A wrote:Hi Katherine!

dS = q/t when you're dealing with a reversible process. dS = nRln(Vf/Vi) when the process is isothermal. dS = nCln(Tf/Ti) when there's a change in temperature associated with the change in entropy. Your C value will change based on whether your volume (Cv) or pressure (Cp) are constant.

Hope that helps!

In the last sentence you said the C value will change depending on whether volume or pressure are constant. Could you elaborate on that?

Zenita Leang 2K
Posts: 67
Joined: Fri Sep 28, 2018 12:28 am

### Re: Delta S equations

If you have a constant volume then you will use Cv which is equivalent to $\frac{3}{2}$R. If it has a constant pressure, then you will use Cp which is equivalent to $\frac{5}{2}$R. R is the constant on the constants and equations sheet.