Science desk
< August 31	<< Aug \| September \| Oct >>	September 2 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

September 1[edit]

Change with temperature of bond energy[edit]

Is the bond energy of a chemical bond dependent on temperature? The calculation of a heat of a reaction based on difference of bond energies compared to usual enthalpy of formation calculations seems to indicate the necessity of bond energy temperature dependence because the enthalpies of reaction are temperature dependent. Is this conclusion valid?--82.137.9.39 (talk) 22:14, 1 September 2016 (UTC)[reply]

There's some discussion of temperature dependence at bond-dissociation energy (which may refer to breaking the first bond, whereas bond energy is an average of all of the same type) I would guess one reason why is that in a hot molecule, the two atoms are in a constant state of vibration along the bond axis. You can think of them as being at rest at the "wrong" distance and having some kinetic energy (i.e. moving) whenever they're at the "right" distance. Wnt (talk) 22:23, 1 September 2016 (UTC)[reply]

The temperature dependence of bond enthalpy is related to heat capacity. See here. As a fundamental concept, it's easiest to explain using the Equipartition theorem. Changes in temperature are divided equally among all degrees of freedom in a molecule, thus when you heat a substance up, some of the heat goes into vibrational modes like bond stretching that would lower the bond dissociation energy of the molecule. I would try to elaborate more, but I have screaming nightmares whenever I try to remember my 20-year old physical chemistry class... --Jayron 32 23:38, 1 September 2016 (UTC)[reply]