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### constant volume vs constant pressure

Posted: 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?

### Re: constant volume vs constant pressure

Posted: Wed Jan 24, 2018 8:01 pm
Yeah, I believe so because otherwise it would cause confusion

### Re: constant volume vs constant pressure

Posted: 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.

### Re: constant volume vs constant pressure

Posted: 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.