## Cp vs Cv

$\Delta U=q+w$

lizettelopez1F
Posts: 29
Joined: Fri Sep 28, 2018 12:19 am

### Cp vs Cv

When would we use the values Cp= (5/2)R and Cv=(3/2)R?

Iona Pay
Posts: 43
Joined: Fri Sep 28, 2018 12:15 am

### Re: Cp vs Cv

It depends on whether the gas in the equation you're working with is under constant pressure (Cp) or constant volume (Cv).

Tameen Ahmed 4C
Posts: 30
Joined: Fri Sep 28, 2018 12:19 am

### Re: Cp vs Cv

It'll be specified in the question! If they say the gas is in constant pressure or constant volume then you would use them

Posts: 91
Joined: Fri Sep 28, 2018 12:16 am

### Re: Cp vs Cv

You use these values when the question involves an ideal gas in thermodynamics. Therefore for a change in entropy question when volume is changing, you can hold pressure constant and use the Cp value in the equation.

Lydia Luong 4L
Posts: 59
Joined: Fri Sep 28, 2018 12:24 am

### Re: Cp vs Cv

Don't worry about it, they will tell you in the question :)

lukezhang2C
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

### Re: Cp vs Cv

Cp represents constant pressure while Cv represents constant volume, our problems will tell us whether or not we would be dealing with constant pressure or volume as one with two changing conditions would be extremely difficult, and would have to use another approach entirely.

Gillian Ward 1F
Posts: 61
Joined: Fri Sep 28, 2018 12:27 am

### Re: Cp vs Cv

Use Cp when there is constant pressure and Cv when there is constant volume. The problem will specify if it is at constant pressure or volume.

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