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Why Does Bond-Breaking Require Energy?

Hi,

Why does breaking chemical bonds require energy? It would be best if you could explain this from a more physics-like perspective.

Thanks.
Reply 1
Avatar for l1lvink
l1lvink
11
This answer won't be very Physics-y, but a bond is the attraction between two electrons, (lets say in a bond of O2) with one electron attracted to each positive nucleus. So in order to break this bond, you have to pull the two electrons apart. In doing this, you have to pull apart the attractive forces, so you exert a force that works against the force of attraction. Hence, you do work, or in other words, energy is used.
Original post by velocitous
Hi,

Why does breaking chemical bonds require energy? It would be best if you could explain this from a more physics-like perspective.

Thanks.


Lets approach this from the opposite perspective. Forming a bond lowers the energy of the system, it releases energy. The arrangement in a chemical bond is lower in energy than 2 isolated atoms.
Why? When two atoms bond, the electron density is concentrated in the space between the two nuclei.

So when breaking the bond you have to put in energy to separate the nuclei.
Reply 3
Avatar for BJack
BJack
19
Original post by l1lvink
This answer won't be very Physics-y, but a bond is the attraction between two electrons, (lets say in a bond of O2) with one electron attracted to each positive nucleus. So in order to break this bond, you have to pull the two electrons apart. In doing this, you have to pull apart the attractive forces, so you exert a force that works against the force of attraction. Hence, you do work, or in other words, energy is used.


This answer is rather confusing. Each electron is attracted to both nuclei, so pulling the two atoms apart (roughly) means losing some of these electron-nucleus attractions because each electron becomes localised on a single atom when the bond is broken. It's definitely not the case that pulling the electrons apart requires you to overcome an attractive force; the two like-charged electrons repel, after all.

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