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### Bond enthalpies

Posted: Thu Jan 30, 2020 3:17 pm
When calculating a reaction using bond enthalpies, will the answer always be negative (exothermic)?

### Re: Bond enthalpies

Posted: Thu Jan 30, 2020 3:48 pm
I don't think so, I'm pretty sure if the energy of the bonds broken is greater than the energy of the bonds formed, then the reaction can be endothermic. But someone correct me if I'm wrong.

### Re: Bond enthalpies

Posted: Thu Jan 30, 2020 3:50 pm
Breaking a bond is endothermic and forming one is exothermic, so it can be either.

### Re: Bond enthalpies

Posted: Thu Jan 30, 2020 6:00 pm
No, when calculating enthalpies of a reaction using bond enthalpies you would add up all the enthalpies of the bonds broken along with all the enthalpies of the bonds formed. If the sum of the enthalpies of the bonds broken are greater than the sum of the bonds formed, then the enthalpy of the reaction is positive and the reaction is endothermic. If the sum of the enthalpies of the bonds formed are greater than the sum of the bonds broken, then the enthalpy of the reaction is negative and the reaction is exothermic. This is because breaking a bond requires energy and forming a bond releases energy.

### Re: Bond enthalpies

Posted: Thu Jan 30, 2020 6:22 pm
it depends on whether or not the value of bonds formed is greater than that of bonds broken.