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Constant Volume vs Constant Pressure

Posted: Sat Jan 20, 2018 12:41 pm
by Helen Shi 1J
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?

Re: Constant Volume vs Constant Pressure

Posted: Sat Jan 20, 2018 1:19 pm
by Sirajbir Sodhi 2K
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.

Re: Constant Volume vs Constant Pressure

Posted: Sat Jan 20, 2018 3:56 pm
by Merzia Subhan 1L
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

Re: Constant Volume vs Constant Pressure

Posted: Sun Jan 21, 2018 9:46 am
by Irma Ramos 2I
Based on the above responses, is it safe to say that there is only work done when there is a change in volume???

Re: Constant Volume vs Constant Pressure

Posted: Sun Jan 21, 2018 4:57 pm
by Leah Thomas 2E
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.

Re: Constant Volume vs Constant Pressure

Posted: Sun Jan 21, 2018 5:00 pm
by Isaiah Little 1A 14B
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.

Re: Constant Volume vs Constant Pressure

Posted: Sun Jan 21, 2018 5:14 pm
by Caroline LaPlaca
w= pdV