Isothermal, Const. P, Const V

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Alex Tchekanov Dis 2k
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Joined: Sat Aug 24, 2019 12:16 am

Isothermal, Const. P, Const V

Postby Alex Tchekanov Dis 2k » Mon Feb 03, 2020 2:04 pm

Could someone please organize all the equations that are specific to a system that has constant Pressure, a system that has constant volume and an isothermal (constant temperate) system. I feel like there are so many equations that get mixed up and I'm not sure when to use which one.

Brian_Ho_2B
Posts: 221
Joined: Fri Aug 09, 2019 12:16 am

Re: Isothermal, Const. P, Const V

Postby Brian_Ho_2B » Mon Feb 03, 2020 3:27 pm

For constant pressure, qp = enthalpy, and qp doesn't necessarily equal delta U. For constant volume, qv = delta U = delta H IF there is no nonexpansion work involved. For isothermal, reversible reactions where delta T is zero, q = -w, delta S = q/T, and
w = -nRTln(V2/V1).

Paul Hage 2G
Posts: 105
Joined: Thu Jul 25, 2019 12:17 am

Re: Isothermal, Const. P, Const V

Postby Paul Hage 2G » Mon Feb 03, 2020 3:28 pm

System with Constant External Pressure: w=-P(external)ΔV
System with Changing Pressure (Reversible Expansion): w=-nRT(ln(V2/V1))
Change in internal energy with ΔP=0 (constant external pressure): ΔU=ΔH-PΔV because q=ΔH and w=-PΔV at constant pressure.


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