Finding bond enthalpies

[Catherine Bubser 2C]

Do we add or subtract reactants from products when obtaining bond enthalpies?

[Aaina 2D]

Hi! We add them together (reactants + products) for bond enthalpies. We break the bonds in the reactants which is an endothermic process. Since it's endothermic, energy needs to be put into the system (makes it positive). In terms of the products, we form new bonds, so energy is released - an exothermic reaction - and makes the bond enthalpies negative. So in a way, we're doing reactants - products to account for the negative bond enthalpies on the products side. Hope this makes sense.

[Katelynn Shaheen 2C]

We add reactants and products when obtaining bond enthalpies.

[DavidTabib 3H]

You add them up after finding the enthalpy for each bond.

[DavidTabib 3H]

You add them up after finding the enthalpy for each bond.

[Lorena_Morales_1K]

Hi! We add them together (reactants + products) for bond enthalpies. We break the bonds in the reactants which is an endothermic process. Since it's endothermic, energy needs to be put into the system (makes it positive). In terms of the products, we form new bonds, so energy is released - an exothermic reaction - and makes the bond enthalpies negative. So in a way, we're doing reactants - products to account for the negative bond enthalpies on the products side. Hope this makes sense.

this answer was super helpful! thank you so much!

[Jarrett Sung 3B]

We add them up because when bonds are formed the deltaH is negative (energy released), while deltaH is positive (energy absorbed) when bonds break.