[poobear]

Hi everyone,

I have a question regarding basically every single chemical reaction, so I don't really know how to ask it, but I ask it with the example of water and oil not mixing.

So, water can do a lot of hydrogen bonding. Oil can not. So water hangs out by himself to maximise the amount of bonds --> lower the energy of the system.

However, as energy can't be destroyed, that bonding energy would be somewhere else if water and oil started to mix. Would it be heat? So why does the energy "prefer" to be in hydrogen bonds compared to heat? From what I'm starting to understand almost everything is due to increasing entropy, is that the answer here as well? However I fail to understand why extra bonds would increase the entropy compared to extra heat.

Thanks!

[Hunter2]

First, mixing of water and oil is not a chemical reaction. Oil is inpolar, water is polar, so the oil moleculs will not dissolve.

[poobear]

Oil is inpolar, water is polar, so the oil moleculs will not dissolve.

I am well aware that "water is polar, so the oil moleculs will not dissolve."
I am asking WHY. Mixing of water and oil would result in LESS favourable bonds, so remanding energy should go somewhere else (heat?). So my question is, why does the energy prefer to be in the bonds rather than heat.

[Dan]

For water and oil to mix, the hydrogen bonds between the water molecules will have to be broken. This requires energy, i.e. you would need to supply energy in order to do it - mixing oil and water would consume heat, not generate it.

You may find this helpful: http://www.chemicalforums.com/index.php?topic=37061.msg141745#msg141745

[poobear]

[...]  i.e. you would need to supply energy in order to do it [...]

Excuse my low level of knowledge, but why do you need to supply energy? All molecules have a great amount of kinetic energy at any relevant temperature. This energy should be enough to break some bonds?

[Dan]

Because you need to break relatively strong bonds to form relatively weak bonds. There is an energy deficit that would have to be met.

You said yourself that the two phase system is at an energetic minimum, and the mixed system would be higher in energy. If you need to go from lower energy to higher energy, then energy must be put in.

Can you explain why you think mixing of oil and water would release energy? I don't understand your logic.