## 3/2R vs 5/2R

$\Delta U=q+w$

Lisa Werner 2F
Posts: 72
Joined: Fri Sep 28, 2018 12:17 am

### 3/2R vs 5/2R

how can we tell when to use 3/2R and 5/2R as C?

Gillian Murphy 2C
Posts: 30
Joined: Fri Sep 28, 2018 12:22 am

### Re: 3/2R vs 5/2R

3/2R is used when it is at constant volume for a monoatomic ideal gas
5/2R is used when it is at constant pressure for a monoatomic ideal gas

Kirsty Star 2H
Posts: 48
Joined: Fri Sep 28, 2018 12:24 am

### Re: 3/2R vs 5/2R

Agreed. You know which one to use in the context of the problem, so it's important to identify what is being held constant in the given problem

Zubair Ahmed 1L
Posts: 81
Joined: Fri Sep 28, 2018 12:16 am

### Re: 3/2R vs 5/2R

It is very important to know the difference between. 5/2R is used for constant pressure and 3/2R is used for constant volume. You will have to use either one depending on the context of the question.

Posts: 33
Joined: Fri Sep 28, 2018 12:22 am

### Re: 3/2R vs 5/2R

Is (3/2 R) the same as Cn when you are trying the change in entropy when there is a temperature difference?

Jason Ye 2I
Posts: 33
Joined: Fri Sep 28, 2018 12:22 am

### Re: 3/2R vs 5/2R

When it is constant pressure or constant volume. Or based on the shape of the molecules.

Soumya Ravichandran 4H
Posts: 62
Joined: Fri Sep 28, 2018 12:19 am

### Re: 3/2R vs 5/2R

3/2 R is used for Cv of an ideal monoatomic atom. 5/2R is for Cv of a linear molecule and for Cp of an ideal monoatomic atom.

Ashe Chen 2C
Posts: 31
Joined: Mon Jan 07, 2019 8:23 am

### Re: 3/2R vs 5/2R

3/2 R is used for a monoatomic ideal gas at constant volume where 5/2 R is used is used for a monoatomic gas at constant pressure, or for a linear molecule at constant volume.

Cameron_Greenberg_3C
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

### Re: 3/2R vs 5/2R

In addition to the other answers, the heat capacity at constant volume and the heat capacity at constant temperature are always separated by a factor of R. (C)v,m = R + (C)p,m. So, for single atoms 3/2R is the (C)v,m and 5/2R is the (C)P,m, while linear atoms have a (C)v,m of 5/2R, and more complicated molecules have a (C)v,m of 3R.