making bonds/breaking bonds and energetics

Woopydalan

Hello,

I have never been able to keep straight in my head if making bonds and breaking bonds are exothermic or endothermic. Is there any way that someone can explain why which is which in a way that is understandable because I'm tired of constantly having to re memorize it.

Ygggdrasil

I always think of it in terms of the Leonard-Jones potential, which describes the energy to two atoms as a function of the distance between them:


The energy of bonded atoms is the energy where the LJ potential is at a minimum, whereas non-bonded atoms are separated by large distances and their energies are found all the way to the far right of the curve. What happens to the energy of two unbonded atoms as they approach each other? Will they need to release energy to the surroundings (because they themselves are decreasing in energy) or do they need to gain energy from the surroundings? For two bonded atoms to become unbonded, will they need to gain energy from their surroundings or release energy to their surroundings?

Woopydalan

Ok just read something that seemed easy to remember...so it's like breaking a window with a hammer. When you break a window, the energy is transferred from the hammer to the window, thus breaking a windows absorbs energy, so breaking a bond absorbs energy, thus endothermic.