units of enthalpy

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Mariane Sanchez 1E
Posts: 57
Joined: Fri Sep 29, 2017 7:07 am

units of enthalpy

Postby Mariane Sanchez 1E » Tue Jan 23, 2018 7:09 pm

when is the unit for the standard enthalpy of formation just kJ and when is it kJ/mol? i noticed in 8.65 that the reactants and products' enthalpy of formation are in kJ/mol, but the enthalpy for the reaction is just in kJ.

Sarah Rutzick 1L
Posts: 50
Joined: Tue Oct 10, 2017 7:13 am

Re: units of enthalpy

Postby Sarah Rutzick 1L » Tue Jan 23, 2018 10:39 pm

The enthalpies of formation for the reactants and products are in kJ/mol because they depend on the number of moles of the reactant or product in the balanced chemical equation. When calculating enthalpy of a reaction from the enthalpies of formation of the reactants and products, you multiply the enthalpy of formation of each reactant/product by the number of moles of that reactant/product in the balanced chemical equation. By doing this, the moles in the enthalpies of formation cancel out, leaving kJ as the final unit for the enthalpy of the reaction.

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