Constant Volume vs Constant Pressure

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Megan Purl 1E
Posts: 49
Joined: Fri Sep 29, 2017 7:07 am

Constant Volume vs Constant Pressure

Postby Megan Purl 1E » Sun Jan 21, 2018 10:29 pm

How does the distinction between constant volume and constant pressure affect the calculations of heat and calorimetry? Which equations are used for constant volume and constant pressure?

Allison Young 1K
Posts: 23
Joined: Fri Sep 29, 2017 7:06 am

Re: Constant Volume vs Constant Pressure

Postby Allison Young 1K » Sun Jan 21, 2018 10:39 pm

Using ΔU = q + w = q - PΔV
For constant volume, ΔU =qv. Because ΔV = 0, w= -PΔV = -P(0) = 0.
For constant pressure, ΔU = ΔH - PΔV, using ΔH = qp.

Rana YT 2L
Posts: 49
Joined: Thu Jul 27, 2017 3:01 am

Re: Constant Volume vs Constant Pressure

Postby Rana YT 2L » Mon Jan 22, 2018 11:10 am

to add onto the previous post,
the actual q equations are the same, you only need to change the value of the specific heat to reflect that of a system under constant pressure or constant volume
q=nCp∆T
or
q=nCv∆T


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