finding enthalpy of non-isobaric process

isochoric/isometric: $\Delta V = 0$
isothermal: $\Delta T = 0$
isobaric: $\Delta P = 0$

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Sue Bin Park 2I
Posts: 52
Joined: Mon Jun 17, 2019 7:24 am

finding enthalpy of non-isobaric process

If we are given a non isobaric process, e.g. an irreversible isothermal expansion, how would we find the enthalpy (delta H) of the process? does delta H exist for a non isobaric reaction?

in particular, i'm dealing with a type of question where you open a valve between two containers of gas. I know deltaH = deltaU + P*deltaV, and in isothermal processes, deltaU = 0. does deltaH just equal work? obviously work wouldn't be defined as P*deltaV though, since this is an irreversible process...or is this just a trick question in asking for delta H? lol

Vincent Leong 2B
Posts: 207
Joined: Fri Aug 09, 2019 12:15 am

Re: finding enthalpy of non-isobaric process

You cant find delta H because enthalpy is heat at constant pressure. To get Delta H you need a constant pressure or else you're solving for q or heat which would be mCdeltaT

VPatankar_2L
Posts: 104
Joined: Thu Jul 25, 2019 12:17 am
Been upvoted: 1 time

Re: finding enthalpy of non-isobaric process

Delta H only = q at constant pressure, so if the pressure is not constant you won't be able to calculate a value for Delta H

Adam Kramer 1A
Posts: 103
Joined: Sat Aug 24, 2019 12:15 am

Re: finding enthalpy of non-isobaric process

You cannot really find the enthalpy at nonisobaric conditions, you would need to find the constant pressure to find the value with the equations we use. Because of this we would need to find heat instead.

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