### Cp or Cv in temperature change

Posted:

**Tue Feb 13, 2018 8:09 pm**When there is a temperature change and we are being asked to solve for delta S, how do we know whether to use Cp or Cv?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=133&t=27726

Page **1** of **1**

Posted: **Tue Feb 13, 2018 8:09 pm**

When there is a temperature change and we are being asked to solve for delta S, how do we know whether to use Cp or Cv?

Posted: **Tue Feb 13, 2018 8:29 pm**

When there are two variables changing like Temperature and Pressure, you would hold the other constant when solving for Delta S when theres change in temp (using equation deltaS=nCpln(T2/T1)

If the two variables are Temperature and Volume you would use the equation deltaS=nCvln(T2/T1)

If the two variables are Temperature and Volume you would use the equation deltaS=nCvln(T2/T1)

Posted: **Mon Mar 12, 2018 9:27 pm**

An easier way to think of it might be that whatever condition is constant is the specific heat used, so if volume is the only variable of the three not changing, you would use Cv in the deltaS equation.

Posted: **Fri Mar 16, 2018 12:41 am**

Based on what information is given, you can tell which variable is staying constant and then accordingly use either Cp or Cv