Bond Enthalpies

[Riya Sood 4G]

Why is calculating enthalpy from bond enthalpies considered to be not as efficient as other methods?

[McKenna_4A]

Because each bond enthalpy AVERAGES can be found on a table. The bond enthalpy of a specific bond depends on the molecule it is in (electrons may be shared unequally). Therefore, using average bond enthalpies will provide an inaccurate value.

[Marni Kahn 1A]

It is also important to take into consideration that some reactions require a change in enthalpy due to a phase change in addition to the substances' bond enthalpies. In this way, Hess's method is more efficient and not as time costly because the enthalpy changes are already given.

[Katie Bart 1I]

Is calculating enthalpy from bond enthalpies more accurate?

[Paul Hage 2G]

Bond enthalpies of diatomic molecules (Br2, I2, Cl2, N2, O2, H2, F2) are accurate because they are measured for those specific molecules; however, all other bond enthalpies are averages from many different molecules, so they are not completely accurate.

[005384106]

For Friday’s lecture when we talked about bond enthalpies, are the energy values for each product and reactant going to be given? How can we solve for these values?

[Jialun Chen 4F]

I agree with McKenna. Due to the numbers given in the bond enthalpy chart being averages, this method is not as accurate relatively.

[Michelle Xie 2B]

The bond enthalpies are averages of all the possible ones, so it is less accurate.

[Shivam Rana 1D]

Using this method is less accurate and takes longer because all the bonds need to be broken and reformed. It is less accurate because the bond enthalpies are averages, not exact values.

[Leila_4G]

Is the table we find this in the textbook or is there a general one online that is the same?

[alicechien_4F]

Is the table we find this in the textbook or is there a general one online that is the same?

I would go with the table in the textbook for homework problems because sometimes the bond enthalpies differ slightly online. It should be roughly the same.

[Emily Chirila 2E]

More accurate methods include Hess’s Method (adding rxns to obtain net rxn) or using ΔH°values from a table