## PV=nRT

nathansalce 3e
Posts: 52
Joined: Thu Jul 27, 2017 3:01 am

### PV=nRT

Can somebody explain the significance of PV=nRT and the role it plays in the chapter. How does it relate to enthalpies? Does it have some relationship to DeltaU=q+w, and can you explain it?

Jessica Yang 1J
Posts: 55
Joined: Fri Sep 29, 2017 7:03 am

### Re: PV=nRT

Hi. I think we use PV=nRT in this chapter to calculate enthalpy. In the example in class today, it says that change in enthalpy = change in internal energy + P (change in V). If we do not know the change in volume of the system and it is not given, we can use the change in moles of gas to calculate the change in enthalpy. The equation would then become change in enthalpy = change in internal energy to (change in n)RT.

Also under constant pressure, work equls -P(change in V), so you could also substitute -(change in n)RT for work as well.

Ya Gao
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am
Been upvoted: 1 time

### Re: PV=nRT

As we know, change in internal energy equals w+q and w=-q*∆V. For gases, when it's under constant pressure and there is a net change in the number of moles, there will be a change in the volume. According to PV=nRT, P∆V=∆nRT. Therefore, when a reaction under constant pressure and has a net change in the number of moles, the work done by the system can be calculated by using ∆nRT.
Hope it helps.

Helen Shi 1J
Posts: 78
Joined: Sat Jul 22, 2017 3:00 am

### Re: PV=nRT

If the system expands or is compressed is there still a change in the net number of moles? If not, would the equation P∆V=∆nRT still hold true because the net number of moles aren't changing?

Julia Cheng 2J
Posts: 31
Joined: Thu Jul 13, 2017 3:00 am

### Re: PV=nRT

If the system expands or is compressed, there can only be a change in the number of moles if the system is open.