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How are qp and qv different?

Posted: Thu Jan 30, 2020 10:37 am
by Bryce Barbee
What is the difference between qc and qv? Do you use both of the as enthalpy in a system?

Re: How are qp and qv different?

Posted: Thu Jan 30, 2020 10:56 am
by Jordan Young 2J
qp is enthalpy at constant pressure and qv is at constant volume. They are used when finding enthalpy/delta H but also find change in internal energy which is q + w so q can either be qp or qv depending on the given conditions

Re: How are qp and qv different?

Posted: Thu Jan 30, 2020 11:10 am
by Abby Soriano 1J
Jordan Young 2J wrote:qp is enthalpy at constant pressure and qv is at constant volume. They are used when finding enthalpy/delta H but also find change in internal energy which is q + w so q can either be qp or qv depending on the given conditions


I know that qp is another way to describe enthalpy, but can qv also be used? If so could you explain how?

Re: How are qp and qv different?

Posted: Fri Jan 31, 2020 12:00 pm
by JasonLiu_2J
qv can also be used to find the enthalpy under the conditions of constant volume. In this scenario, you would need to use the equation ∆H=∆U + ∆PV. Remember that ∆U=q+w, and at constant volume, w=0 (since w=P∆V). As such, you find that ∆U=qv, and the equation for enthalpy change becomes ∆H=qv+V∆P, where volume is a constant and the pressure changes.