# specific Bond energies **URL:** \ **Category:** Factual Questions\ **Created:** [January 27, 2003, 10:18pm UTC](https://boards.straightdope.com/t/specific-bond-energies/151344 "2003-01-27T22:18:51Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Grievar](https://avatars.discourse-cdn.com/v4/letter/g/82dd89/32.png) [@Grievar](https://boards.straightdope.com/u/Grievar)\ **Post date:** [January 27, 2003, 10:18pm UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/1 "2003-01-27T22:18:51Z")
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? ---
**Author:** ![Grievar](https://avatars.discourse-cdn.com/v4/letter/g/82dd89/32.png) [@Grievar](https://boards.straightdope.com/u/Grievar)\ **Post date:** [January 30, 2003, 3:23pm UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/2 "2003-01-30T15:23:54Z")
bump? ---
**Author:** ![II\_Gyan\_II](https://avatars.discourse-cdn.com/v4/letter/i/bbe5ce/32.png) [@II\_Gyan\_II](https://boards.straightdope.com/u/II_Gyan_II)\ **Post date:** [January 30, 2003, 3:42pm UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/3 "2003-01-30T15:42:37Z")
> [@](#): > > \*Originally posted by Grievar \* > \*\*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? \*\* 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. ---
**Author:** ![Grievar](https://avatars.discourse-cdn.com/v4/letter/g/82dd89/32.png) [@Grievar](https://boards.straightdope.com/u/Grievar)\ **Post date:** [January 30, 2003, 4:15pm UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/4 "2003-01-30T16:15:18Z")
I was wondering if you could calculate bond enthalpy using electronegativity, hybridization, and radius, but I guess not. ---
**Author:** ![Grievar](https://avatars.discourse-cdn.com/v4/letter/g/82dd89/32.png) [@Grievar](https://boards.straightdope.com/u/Grievar)\ **Post date:** [January 30, 2003, 4:28pm UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/5 "2003-01-30T16:28:29Z")
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. ---
**Author:** ![Grievar](https://avatars.discourse-cdn.com/v4/letter/g/82dd89/32.png) [@Grievar](https://boards.straightdope.com/u/Grievar)\ **Post date:** [January 31, 2003, 1:21am UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/6 "2003-01-31T01:21:19Z")
bump? ---
**Author:** ![banks](https://avatars.discourse-cdn.com/v4/letter/b/278dde/32.png) [@banks](https://boards.straightdope.com/u/banks)\ **Post date:** [January 31, 2003, 2:53am UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/7 "2003-01-31T02:53:01Z")
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. ---
**Author:** ![Giraffe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giraffe/32/129_2.png) [@Giraffe](https://boards.straightdope.com/u/Giraffe)\ **Post date:** [January 31, 2003, 3:29am UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/8 "2003-01-31T03:29:41Z")
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. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [January 31, 2003, 7:08am UTC](https://boards.straightdope.com/t/specific-bond-energies/151344/9 "2003-01-31T07:08:29Z")
Energy. Bond energy.