### 9.7

Posted:

**Thu Feb 01, 2018 9:15 pm**Does anyone understand the equation Cp=5/2R? It is used in this problem and I don't understand what this equation is and why we need to use it for this problem.

Thanks!

Thanks!

Created by Dr. Laurence Lavelle

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

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=131&t=26706

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Posted: **Thu Feb 01, 2018 9:15 pm**

Does anyone understand the equation Cp=5/2R? It is used in this problem and I don't understand what this equation is and why we need to use it for this problem.

Thanks!

Thanks!

Posted: **Thu Feb 01, 2018 9:17 pm**

This gives us the heat capacity for an ideal gas at constant pressure so we use it so we can plug it into our entropy equation to solve.

Posted: **Thu Feb 01, 2018 9:24 pm**

how do you know when you are suppose to use the fractions?

Posted: **Thu Feb 01, 2018 9:40 pm**

We can substitute the expressions for the heat capacities at both constant volume and pressure if we are aware of the molecular complexity. This means classifying the substance as monatomic, linear molecule, or nonlinear molecule.

Posted: **Fri Feb 02, 2018 10:28 am**

Also, the value of Cp as well as Cv will be given to us on exams.

Posted: **Fri Feb 02, 2018 12:01 pm**

I’m confused about what does the fraction means

Posted: **Fri Feb 02, 2018 12:33 pm**

I don't think we have to necessarily know the details of how we get the fractions, but pages 277 and 281 in the textbook explain what those values are and how they come to be.

Posted: **Sat Feb 03, 2018 2:17 pm**

We just need to know that its for a monatomic ideal gas atom. The C=5/2 R is on the formula sheet if I remember correctly!