Units for heat of reaction

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Tyler Angtuaco 1G
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Joined: Wed Sep 11, 2019 12:16 am

Units for heat of reaction

Postby Tyler Angtuaco 1G » Fri Feb 07, 2020 8:36 pm

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?

Jonathan Gong 2H
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Joined: Sat Jul 20, 2019 12:16 am

Re: Units for heat of reaction

Postby Jonathan Gong 2H » Fri Feb 07, 2020 10:57 pm

I'm not sure exactly what you are asking for; however, kJ/mol is a perfectly valid unit.

Osvaldo SanchezF -1H
Posts: 122
Joined: Wed Sep 18, 2019 12:21 am

Re: Units for heat of reaction

Postby Osvaldo SanchezF -1H » Fri Feb 07, 2020 10:59 pm

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.

Shutong Hou_1F
Posts: 117
Joined: Sat Sep 14, 2019 12:17 am

Re: Units for heat of reaction

Postby Shutong Hou_1F » Sat Feb 08, 2020 12:44 am

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.

Maika Ngoie 1B
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Joined: Fri Aug 02, 2019 12:16 am

Re: Units for heat of reaction

Postby Maika Ngoie 1B » Sat Feb 08, 2020 12:40 pm

Yup! The standard enthalpy of formation for products and/or reactants should be in kJ/mol

805097738
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Joined: Wed Sep 18, 2019 12:20 am

Re: Units for heat of reaction

Postby 805097738 » Sat Feb 08, 2020 3:40 pm

do you have to explicitly state per mole or is that implied already

Rory Simpson 2F
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Joined: Fri Aug 09, 2019 12:17 am

Re: Units for heat of reaction

Postby Rory Simpson 2F » Sat Feb 08, 2020 3:45 pm

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.

Altamash Mahsud 1I
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Joined: Fri Aug 09, 2019 12:16 am

Re: Units for heat of reaction

Postby Altamash Mahsud 1I » Sat Feb 08, 2020 4:22 pm

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.

kristi le 2F
Posts: 102
Joined: Thu Jul 11, 2019 12:15 am

Re: Units for heat of reaction

Postby kristi le 2F » Sun Feb 09, 2020 10:06 pm

Also, if you keep track of units, it makes it easier to do any calculations you may need.

Jamie Hwang 2F
Posts: 104
Joined: Thu Jul 25, 2019 12:16 am

Re: Units for heat of reaction

Postby Jamie Hwang 2F » Sun Feb 09, 2020 10:29 pm

cancelling units when you solve the problem and keeping track of them is what I do to get the final units


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