constant volume vs constant pressure

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Sophie Krylova 2J
Posts: 59
Joined: Fri Sep 29, 2017 7:06 am

constant volume vs constant pressure

Postby Sophie Krylova 2J » Wed Jan 24, 2018 7:58 pm

So whenever we are told that pressure or volume is constant, do we automatically assume that the other isn't?

Abdullah2I
Posts: 41
Joined: Fri Sep 29, 2017 7:06 am

Re: constant volume vs constant pressure

Postby Abdullah2I » Wed Jan 24, 2018 8:01 pm

Yeah, I believe so because otherwise it would cause confusion

Sammy Thatipelli 1B
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Joined: Thu Jul 27, 2017 3:01 am
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Re: constant volume vs constant pressure

Postby Sammy Thatipelli 1B » Thu Jan 25, 2018 1:17 pm

Yes, you would because there are different equations for constant pressure or constant volume. If the case were constant pressure you would have to know that deltaH=Qp, so internal energy for example would be deltaU=deltaH. If the case were constant volume, you would use Q=deltaH-PdeltaV. These equations, and the ones for constant volume or pressure of an ideal gas (where there are different heat capacities depending on constant pressure or volume), can help you to know that when a situation cannot be constant pressure, it must be constant volume, because we have different equations for each unique situation. there is no equation that we have learned that ties in together both pressure and volume as constant.

Swetha Sundaram 1E
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Re: constant volume vs constant pressure

Postby Swetha Sundaram 1E » Thu Jan 25, 2018 2:02 pm

Yes I agree with Sammy. Also note that when they say mention constant pressure in the problem. The Specific Heat Capacity can be found by 5/2 multipled by R. And for constant volume the specific heat capacity can be found by 3/2 multiplied by R.


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