## PV = nRT

$\Delta U=q+w$

Lauryn Jordan 1F
Posts: 76
Joined: Fri Sep 29, 2017 7:07 am

### PV = nRT

when do you use PV = nRT?

Kaylin Krahn 1I
Posts: 57
Joined: Fri Sep 29, 2017 7:04 am
Been upvoted: 1 time

### Re: PV = nRT

When dealing with an ideal gas and if you are looking for one of the variables and given the others. You're not really directed to use it, but you use it to find a missing variable that you might need. For example, if you need to use volume but you're given moles, temperature, and pressure. Also, work is equal to both -p delta v and -nRT so it depends on what you're given.

Beza Ayalew 1I
Posts: 58
Joined: Fri Sep 29, 2017 7:07 am

### Re: PV = nRT

if you're using delta v, you're probably going to be using delta nRT, so that something to consider as well

Beza Ayalew 1I
Posts: 58
Joined: Fri Sep 29, 2017 7:07 am

### Re: PV = nRT

Also can someone explain why you have delta nRT, but not nRdeltaT? I feel like I've seen the second one being used but usually the change goes towards the number of moles.

Angela G 2K
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

### Re: PV = nRT

Delta nRT is used to calculate the change in internal energy under constant pressure. Delta U = q + w, but under constant pressure it becomes
$\Delta U=\Delta H-P\Delta V$

A change in volume is often due to a net change in gas molecules, so $P\Delta V=\Delta nRT$. Substitute in and you get $\Delta U=\Delta H-\Delta nRT$.

Jennie Fox 1D
Posts: 66
Joined: Sat Jul 22, 2017 3:01 am

### Re: PV = nRT

For ideal gases when you need to solve for a constant.

mayapartha_1D
Posts: 50
Joined: Fri Sep 29, 2017 7:07 am

### Re: PV = nRT

You use this equation for ideal gases! If in a problem, you are given a pressure and the other variables, and it is stated that the given substance is an ideal gas, you will use this equation.

Hope this helped,
Maya