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finding enthalpy of non-isobaric process

Posted: Wed Feb 12, 2020 1:50 pm
by Sue Bin Park 2I
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

Re: finding enthalpy of non-isobaric process

Posted: Thu Feb 13, 2020 10:44 am
by Vincent Leong 2B
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

Re: finding enthalpy of non-isobaric process

Posted: Sat Feb 15, 2020 4:18 pm
by VPatankar_2L
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

Re: finding enthalpy of non-isobaric process

Posted: Thu Feb 20, 2020 8:04 am
by Adam Kramer 1A
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.