Heat Capacity of Air at Constant Volume

  • Thread starter s.p.q.r
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  • #1
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Hi

I have an ongoing dispute with my mate on this one, please help to clarify this before I open up a can of whoop ass on that sorry mo-fo.


300 litres of air are compressed into a 3 litre tank. What is the heat capacity of this air?

Thanks in advance.
 

Answers and Replies

  • #2
Hootenanny
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What do you think it is?
 
  • #3
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The Cp J mol is 29.19. But because I ask for constant volume, it is definately lower then this. This is what I think. I can find no references to constant volume anywhere and unfortunately I have no teacher to ask as I study archaeology, not physics.

Do you have the answer?


Thanks in advance.
 
  • #4
Andrew Mason
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The Cp J mol is 29.19. But because I ask for constant volume, it is definately lower then this. This is what I think. I can find no references to constant volume anywhere and unfortunately I have no teacher to ask as I study archaeology, not physics.

Do you have the answer?


Thanks in advance.
Air is almost entirely a diatomic gas, [itex]\gamma = C_p/C_v = 1.4[/itex] (7/5)

AM
 
  • #5
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Hi,


Thanks for the reply. Is 1.4 per gram or mol?

Also,

How can you measure a gram of gas and how much is 1 mol?

Cheers.
 
  • #7
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Is heat capacity independent of volume for an ideal gas?

Stupid question - gas performs work while being compressed.
 
Last edited:
  • #8
mgb_phys
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For an ideal gas heat capcity just depends on the amount (number of moles) present and the number of vibration states of the molecular.
For a real gas it also depends on the pressure because the molecules close to each other change the vibration state/bond energy.
 
  • #9
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In a modification of the "ideal gas" law, I seem to recall an equation with correction terms for the volume and pressure, respectively. Has anyone run across this?
 
  • #10
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Hi,
This ratio of 1.4, does this just mean that you divide the constant pressure capacity (1.020J/g) by 1.4?
 
  • #11
Andrew Mason
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Hi,
This ratio of 1.4, does this just mean that you divide the constant pressure capacity (1.020J/g) by 1.4?
[itex]\gamma = 1.4[/itex] is the ratio of the specific heat (heat flow per gram or per mole per degree K change in temperature) at constant pressure to the specific heat at constant volume. [itex]\gamma = C_p/C_v[/itex]. What you want to find is Cv. You also have to find the number of moles of air in this container to find its heat capacity (heat flow per degree K change in Temp.).

AM
 
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