# Release or absortion of energy on bonds and phase change

Tags:
1. Nov 13, 2015

### FG_313

I believe I can explain why there is energy needed to break intermoleculares bonds and getting into a gas or liquid, but the other way around confuses me. Bonds have potential energy associated to it, so It's needed work to break the bonds, because we would be trying to move a molecule away from a lower potential energy to a higher, like lifting an object. (Is that correct?) Now the other way confuses me, if the molecules get less kinetic energy when heat is transfered to the outside of the system, and than they get closer together so the bonds "stick" or if the bonds being created is what gives heat to the surroundings. If I'm completaly wrong in those explanations please let me know and explain it to me, or refer me to an adequate material.

2. Nov 14, 2015

### Staff: Mentor

To be honest I have no idea what the problem is. However, if you have no problems understanding the process when it goes one way, simply reverse everything - and you have the reverse process.

Both. Removing kinetic energy is cooling the gas/liquid, energy of bonds is a latent heat.

3. Nov 14, 2015

### FG_313

Thank you, but the reason for the question is that I dont understand why there is a release of energy when intermolecular bonds are made (why we need to cool a liquid for it to solidificate). There is a need for cooling because the molecules have to be closer together and with low energy so that the bonds can be made or there is a need for energy release in the forming of the bonds. If the second or, like you said, both are true, what in the formation of bonds is responsable for the energy release and please describe how that happens. There is work/energy needed to separate two molecules and make them free (gas/liquid), and I attempted to understand it in therms of eletromagnetic forces, but why the forming releases energy is what I dont understand, in therms of forces, energy and potencial.

4. Nov 15, 2015

### Staff: Mentor

In general breaking any bond requires energy, and the opposite - energy being produced when the bond is created - is also true. Technically these are identical processes, just running in different directions.

Intermolecular bonds are not much different in this aspect from other bonds, the main difference is their (typically much lower) strength.