Bond Enthalpies

[Lexie Baughman 2C]

Just confirming - when using the bond enthalpies method, it's the sum of the bonds broken minus the sum of the bonds formed, right? This goes against the sum of products minus the sum of reactants in other forms of the equation, so I wanted to make sure I have it right. Thanks!

[Mindy Kim 4C]

Yes, you are correct. The bonds broken require energy so they are positive while when bonds are formed energy is released so deltaH is negative.

[Arianna Ko 2E]

It takes more energy to break the bonds, thus breaking the bonds is an endothermic reaction. Forming is the bonds is an exothermic reaction, so the equation to find the total bond enthalpy is in the fact bonds broken - bonds formed.

[Anmol_cheema_2F]

Yes, thats right. The bonds broken (reactants) require energy and are endothermic/positive. The bonds formed (products) release energy and are exothermic/negative.

[Saman Andalib 1H]

Yes, you are correct. The formula is the summation of the bonds broken minus the summation of the bonds formed.

[Timothy_Yueh_4L]

You are correct, we use this convention because all bond enthalpies given are positive and when bonds are broken, energy is required into the system therefore the H is positive and when bonds are formed, energy is released therefore H is negative so a negative sign is placed in front of the sum of bonds formed. Since enthalpy is a state function, which disregards the path taken, you add the bonds broken and bonds formed together and get: (delta H) = ((delta H)[BROKEN]) + (-(delta H)[FORMED]), resulting in BONDS BROKEN - BONDS FORMED.

[anthony_trieu2L]

In addition, this method is the least accurate because we are calculating the average bond enthalpies of each bond from different molecules. Therefore, there will always be some error in the final value.

[Jack Hewitt 2H]

Yes, the bonds broken release energy (reactants) and the bonds formed require energy (products).

[jlinwashington1B]

Yes, thats right !