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### Standard Enthalpies of Formation

Posted: Sun Jan 21, 2018 3:54 pm
So when calculating the total enthalpy of a reaction and we are given standard enthalpies of formation of the individual products and reactants all we need to do from there is add up the bonds formed in the products and the bonds broken in the reactants and subtract the total enthalpy of the formed bonds by the broken bonds?

### Re: Standard Enthalpies of Formation

Posted: Sun Jan 21, 2018 4:48 pm
the two are different but that's how you would do a calculation of the enthalpy of reaction through bond enthalpies

### Re: Standard Enthalpies of Formation

Posted: Sun Jan 21, 2018 4:50 pm
Using standard enthalpies of formation and using bond enthalpies are actually two different methods of calculating the enthalpy of the reaction. If you are given standard enthalpies of formation (SEF), do the sum of the SEF of the products minus the sum of the SEF of the reactants to get the enthalpy of the reaction. This is more accurate than using bond enthalpies (BE), but if you are given BE, you do the sum of the BE of the bonds broken minus the sum of the BE of the bonds formed.

### Re: Standard Enthalpies of Formation

Posted: Sun Jan 21, 2018 4:56 pm
Multiply the standard enthalpies of formation times the number of moles for the products and add them all together. Do the same for the reactants. Then, subtract the total of the products by the total of the reactants.