Reaction Enthalpies: When kJ and when kJ/mol?

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Maggie Miller 2K
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Joined: Fri Jun 17, 2016 11:28 am

Reaction Enthalpies: When kJ and when kJ/mol?

Postby Maggie Miller 2K » Tue Jan 17, 2017 10:54 pm

In several of the chapter 8 homework problems we have had to do, sometimes the reaction enthalpy will need to be in kJ/mol, often in order to continue the problem and result in just kJ, but sometimes it does not.

I am confused by when kJ or kJ/mol is used with standard reaction enthalpies because it doesn't seem to make sense to use kJ/mol with reaction enthalpies. My reasoning comes from the idea that if the reaction had a different ratio of moles of substances (i.e. 3:3:6 vs 1:1:6), the result of the standard reaction enthalpy would be different for each situation.

Does anyone know the answer to this?

Thank you!!

Simone Seliger 1C
Posts: 30
Joined: Fri Sep 25, 2015 3:00 am

Re: Reaction Enthalpies: When kJ and when kJ/mol?

Postby Simone Seliger 1C » Tue Jan 17, 2017 11:32 pm

If you get the answer in kJ/mol then it is in standard heat capacity, which assumes it is per mole. If it is in kJ, then it is not in standard form and has been adjusted for the fact that the amount of the substance in question is greater or less than one mole. This would entail finding the moles of the mass, then multiplying that by your kJ/mol answer, thus canceling out the unit mole.

Hope this helps!

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