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Units for heat of reaction

Posted: Fri Feb 07, 2020 8:36 pm
by Tyler Angtuaco 1G
If you are given the heat of reaction in kJ but want to express it in terms of a reactant or product, is it correct to write "kJ per mole of said reactant or product?" Or is this an invalid statement?

Re: Units for heat of reaction

Posted: Fri Feb 07, 2020 10:57 pm
by Jonathan Gong 2H
I'm not sure exactly what you are asking for; however, kJ/mol is a perfectly valid unit.

Re: Units for heat of reaction

Posted: Fri Feb 07, 2020 10:59 pm
by Osvaldo SanchezF -1H
If you want to do it in terms of product or reactant it would also be in terms of KJ/mole and that is called the heat of formation for the product or reactant.

Re: Units for heat of reaction

Posted: Sat Feb 08, 2020 12:44 am
by Shutong Hou_1F
I think that the unit should just be kJ/mol, because I think that adding or removing something from a unit would make things weird and even the unit invalid. If you want specify that you are calculating enthalpy of formation of a particular substance, you could specify that at the beginning of your equation, right after delta H rxn and before the = sign.

Re: Units for heat of reaction

Posted: Sat Feb 08, 2020 12:40 pm
by Maika Ngoie 1B
Yup! The standard enthalpy of formation for products and/or reactants should be in kJ/mol

Re: Units for heat of reaction

Posted: Sat Feb 08, 2020 3:40 pm
by 805097738
do you have to explicitly state per mole or is that implied already

Re: Units for heat of reaction

Posted: Sat Feb 08, 2020 3:45 pm
by Rory Simpson 2F
805097738 wrote:do you have to explicitly state per mole or is that implied already


You should explicitly state it per mole in the case of standard reaction enthalpy or standard formation enthalpy because those are definitionally for one mole of a compound. I guess it's mostly for the consistency of units, though.

Re: Units for heat of reaction

Posted: Sat Feb 08, 2020 4:22 pm
by Altamash Mahsud 1I
Yes, for the heat of reaction, you must state it in kj/mol because in a reaction, there could be 2 moles of a reactant being used to form a product, and in that case, the per mole part of the heat of reaction matters, because in that case you must divide the amount of heat by two. So yes, the per mole of reactant or product matters.

Re: Units for heat of reaction

Posted: Sun Feb 09, 2020 10:06 pm
by kristi le 2F
Also, if you keep track of units, it makes it easier to do any calculations you may need.

Re: Units for heat of reaction

Posted: Sun Feb 09, 2020 10:29 pm
by Jamie Hwang 2F
cancelling units when you solve the problem and keeping track of them is what I do to get the final units