## Regarding the equation deltaS=nCln(Tf/Ti)

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

Lizzie Zhang 2C
Posts: 31
Joined: Fri Sep 29, 2017 7:05 am

### Regarding the equation deltaS=nCln(Tf/Ti)

For the formula nCln(Tf/Ti), if we were to calculate entropy change for a liquid or solid state substance, do we plug in the heat capacity for that substance in liquid/solid state? I thought Cv or Cp is only used for gases.

Thanks!

Laura Riccardelli
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

### Re: Regarding the equation deltaS=nCln(Tf/Ti)

If you look at problem 9.19 they give you the Cp for liquid and vapor water so I am assuming that the equation can be used for nay state as long as they give you the Cv/Cp for the problem.

melissa carey 1f
Posts: 53
Joined: Fri Sep 29, 2017 7:06 am

### Re: Regarding the equation deltaS=nCln(Tf/Ti)

Also, when do we need to include n, the number of moles, as I see it omitted in some forms of the equations? Thanks!

JamesAntonios 1E
Posts: 70
Joined: Fri Sep 29, 2017 7:04 am

### Re: Regarding the equation deltaS=nCln(Tf/Ti)

melissa carey 1f wrote:Also, when do we need to include n, the number of moles, as I see it omitted in some forms of the equations? Thanks!

You pretty much always include them for entropy calculations. Because the units have to cancel out to leave you with J/K.