Constant Volume vs Constant Pressure

Moderators: Chem_Mod, Chem_Admin

Helen Shi 1J
Posts: 78
Joined: Sat Jul 22, 2017 2:00 am

Constant Volume vs Constant Pressure

Postby Helen Shi 1J » Sat Jan 20, 2018 12:41 pm

I am a little confused about how systems under constant volume differ from those under constant pressure. For systems under constant volume, how is pressure changing and how do we find the work enacted on the system?

Sirajbir Sodhi 2K
Posts: 47
Joined: Sat Jul 22, 2017 2:00 am

Re: Constant Volume vs Constant Pressure

Postby Sirajbir Sodhi 2K » Sat Jan 20, 2018 1:19 pm

For systems that are at constant volume, no work is done, since the change in volume is 0 (w = - (external pressure) * change in volume). In these systems, pressure increases as a result of heat. We know that pressure increases because of Boyle's law.

For systems at constant pressure, work is being done as the volume is changed and we know this from the equation above.

Merzia Subhan 1L
Posts: 33
Joined: Thu Jul 13, 2017 2:00 am

Re: Constant Volume vs Constant Pressure

Postby Merzia Subhan 1L » Sat Jan 20, 2018 3:56 pm

When volume is constant, Delta V is 0 because delta V is final volume - initial volume. The formula for work, stated above, would indicate that work is then 0. If pressure is constant, work could still be done, if volume changes as well

Irma Ramos 2I
Posts: 51
Joined: Fri Sep 29, 2017 6:07 am

Re: Constant Volume vs Constant Pressure

Postby Irma Ramos 2I » Sun Jan 21, 2018 9:46 am

Based on the above responses, is it safe to say that there is only work done when there is a change in volume???

Leah Thomas 2E
Posts: 51
Joined: Fri Sep 29, 2017 6:06 am

Re: Constant Volume vs Constant Pressure

Postby Leah Thomas 2E » Sun Jan 21, 2018 4:57 pm

Yes to the above answer. Work can be done by the system or unto the system based on expansion or compression which is a change in volume. Just be wary of open and closed systems.

Isaiah Little 1A 14B
Posts: 50
Joined: Fri Sep 29, 2017 6:05 am

Re: Constant Volume vs Constant Pressure

Postby Isaiah Little 1A 14B » Sun Jan 21, 2018 5:00 pm

Because W (work) = PdV (pressure times a change in volume), work cannot be done if there is no change in volume since the dV value would equal 0.

Caroline LaPlaca
Posts: 30
Joined: Sat Jul 22, 2017 2:01 am

Re: Constant Volume vs Constant Pressure

Postby Caroline LaPlaca » Sun Jan 21, 2018 5:14 pm

w= pdV


Return to “Heat Capacities, Calorimeters & Calorimetry Calculations”

Who is online

Users browsing this forum: No registered users and 2 guests