specific Bond energies

Factual Questions
1

How do you figure out the bond energy of a specific bond in a
specific molecule, rather than just the average?

Like what’s the bond energy/enthalpy of the OH in nitric acid versus
the OH in water?

2

bump?

3

It’s been a looooooooooonnnnggg time since I did this physical/inorganic chemistry.

If you mean mathematically from the average, you can’t.

I guess you try to reduce it or oxidise it using the correctly attacking agents and then see the energy change.

But, someone current should answer this.

4

I was wondering if you could calculate bond enthalpy using
electronegativity, hybridization, and radius, but I guess not.

5

well the way I see it.

if the bond enthalpy of C-H in CH4 is X, then in CH2O it would be
Y amount more than X since the electronegative O polarizes the
rest of the molecule, and I figure the more polarized a bond is, the
harder it is to break.

Now I figure you could play around with the radii and electro
negativities of the atoms and come up with a number for the
approximate bond energy.

6

bump?

7

Simple answer: Experimentally.
AFAIK, it’s really difficult to get a calculated value. I remember an equation from physical chemistry to estimate it, but the margin of error was pretty large. You could also build the molecule in question in Gaussian, or maybe Spartan if you’re feeling masochistic, and ask said program to find the bond enthalpy for you. But you still get a pretty big error bar.
Really, the only way to get remotely accurate numbers would be experimentally.
But I’m going to go see if I can find that equation. I’ll get back to you.

8

Simply put, this is a hard thing to do, and it depends on the system. There are a host of numerical techniques, with varying degrees of accuracy depending on the system. Density Functional Theory does well in a lot of cases, and is completely wrong in others. Quantum Monte Carlo does very well in some cases.

There is certainly no analytic theory involving radii and electronegativity that is going to be more than a gross approximation. Maybe good for an order of magnitude estimate, nothing more.

9

Energy. Bond energy.