I spied a nit at which I must pick. This is something that’s become ingrained in certain science discussions, one of those innocent things that may or may not propagate a misconception and I’m sure it rarely causes an eyebrow to be raised, but, dammit, someone’s wrong on the internet.

Someone will tell me that energy is obtained because you’ve broken a chemical bond. It happens often enough that it’s not worth mentioning where I saw it (OK, OK, I’ll talk. It was Schwartz Matt) But seriously, it’s something you’ll run across a lot if you read stories about chemical processes and energy.

It’s one of those things that can be true but isn’t generally true. And the overall implication — that there is energy stored in the bonds which is released when you break them — is flat-out wrong.

Forming a bound state releases energy. Breaking apart that bound state requires the addition of energy. We can quantify the tightness of the bond by how much energy is involved, and that’s what we do with the enthalpy of formation: you have a baseline system — the free gases and atoms with which you start — which has (what we define as) zero energy. If you want to go from one bound system to another, you will release the difference in the enthalpies, because energy is conserved. (And if you look at more complex systems you involve the more and more complicated energies you find in thermodynamics) But the release of energy is in the formation of new, tighter bonds that are present in the products — that’s where the energy comes from. Burning those hydrocarbons is releasing energy not because you are breaking the bonds with the carbon and hydrogen, but because the bonds with the oxygen are stronger, and forming them releases the energy.