Different Molar Heat Capacities For Gases

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Yang Chen 2E
Posts: 36
Joined: Thu Jul 13, 2017 3:00 am

Different Molar Heat Capacities For Gases

Postby Yang Chen 2E » Fri Jan 12, 2018 2:13 pm

I'm still extremely confused on how gases could have multiple molar heat capacities. If you were to change the pressure or volume of a gas, you technically don't have to change the amount of moles of gas within the container right?

Sara Varadharajulu
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Re: Different Molar Heat Capacities For Gases

Postby Sara Varadharajulu » Fri Jan 12, 2018 3:36 pm

I think when the volume is not constant (like with a piston), you need to take into account work (to move the piston?). im not quite sure though.

Christine Wastila 1H
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Joined: Fri Sep 29, 2017 7:04 am

Re: Different Molar Heat Capacities For Gases

Postby Christine Wastila 1H » Fri Jan 12, 2018 3:48 pm

Cv denotes the heat capacity of a gas at a constant volume while Cp denotes the heat capacity of a gas at constant pressure. We have two values because, when heating takes place at constant pressure, some of the heat is used to do expansion work rather than raise the temperature of the system. For a more thorough explanation, read section 8.9 in the textbook.

Maria Bajenov 1I
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Re: Different Molar Heat Capacities For Gases

Postby Maria Bajenov 1I » Sat Jan 13, 2018 10:31 am

For measuring heat transfer, the equation q=(n)(Cp)(delta T) relates molar heat capacity at a constant pressure with moles. If one were to change, the other would change accordingly. The relation changes if it is at constant volume instead.

Yang Chen 2E
Posts: 36
Joined: Thu Jul 13, 2017 3:00 am

Re: Different Molar Heat Capacities For Gases

Postby Yang Chen 2E » Sun Jan 14, 2018 12:10 am

I'm still confused on the reason why there are two separate molar heat capacities. I know that substances expand when heated which would change the heat capacity assuming we have constant pressure, but what happens if we have a constant volume? How would having a constant volume affect molar heat capacity for a gas?

Kyle Sheu 1C
Posts: 87
Joined: Fri Jun 23, 2017 11:39 am

Re: Different Molar Heat Capacities For Gases

Postby Kyle Sheu 1C » Sun Jan 14, 2018 3:36 pm

The molar heat capacity at constant volume would be lower than that at constant pressure because all the heat goes into increasing the internal energy.


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