finding enthalpy of non-isobaric process


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

finding enthalpy of non-isobaric process

Postby Sue Bin Park 2I » Wed Feb 12, 2020 1:50 pm

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
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Joined: Fri Aug 09, 2019 12:15 am

Re: finding enthalpy of non-isobaric process

Postby Vincent Leong 2B » Thu Feb 13, 2020 10:44 am

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

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Re: finding enthalpy of non-isobaric process

Postby VPatankar_2L » Sat Feb 15, 2020 4:18 pm

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
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Joined: Sat Aug 24, 2019 12:15 am

Re: finding enthalpy of non-isobaric process

Postby Adam Kramer 1A » Thu Feb 20, 2020 8:04 am

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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