## Constant Pressure vs Constant Volume

Rosa Munoz 2E
Posts: 105
Joined: Wed Sep 18, 2019 12:21 am

### Constant Pressure vs Constant Volume

Can someone explain the key differences

Sanjana Munagala_1j
Posts: 103
Joined: Sat Aug 24, 2019 12:17 am
Been upvoted: 1 time

### Re: Constant Pressure vs Constant Volume

At constant Pressure:
q= change in H
Change in U= q + w
w= -P(change in V)

At constant volume:
Change in u= q
w=0

I am not sure if I hit everything, but I hope this gives you some idea.
Hope this helps!

Hussain Chharawalla 1G
Posts: 100
Joined: Sat Jul 20, 2019 12:15 am

### Re: Constant Pressure vs Constant Volume

An open system will have constant pressure, and a closed system will have constant volume.

805307623
Posts: 99
Joined: Fri Aug 09, 2019 12:17 am

### Re: Constant Pressure vs Constant Volume

For constant pressure and constant volume, the heat exchanged is proportional to the difference in temperature and the amount of gas. The proportionality constant is Cp for the process at constant pressure and Cv for the process at constant volume. The major difference between the two is that work is associated to the process at constant pressure, but is zero in the process at constant volume.
Constant pressure: W = P * (Vfinal - Vinitial)
Constant Volume: W = 0

Dan M -3E
Posts: 101
Joined: Wed Sep 18, 2019 12:19 am

### Re: Constant Pressure vs Constant Volume

You can also get the amount of work thru the graphs, because the area under the pressure-volume graph is equal to the work. So, when volume is constant, the graph is a vertical line, and there is no area underneath and therefore no work done. When pressure is constant, the area underneath is a square of area=(constants pressure)*(volume change), or in other words, W=p*deltaV.