# Does dissociation happen in gases?

I understand that dissociation is when something dissolve. I heard this mostly only happen in liquids. But now I heard it can also happen in gases. Is this true? If so, when and why does this happen, and does it only happen to certain gases? I tried to do research but didn't find too much information. The only real information I found was on Wikipedia and it was confusing.

• What information? Also are you asking about homo- or heterolytic dissociation? – Mithoron Jun 25 '16 at 0:36
• Dissociation is a common way for things to be dissolved in liquids. In gases, things may dissociate but the mechanism is not about interaction with other things in the gas but because some molecules are unstable and may fall apart into other molecules depending on pressure and temperature. A famous example is dinitrogen tetroxide which dissociates at higher temperatures into nitrogen dioxide. – matt_black Jun 25 '16 at 10:19

The information is confusing precisely because your question itself is confusing. There are different kinds of dissociation, and different degrees thereof. Moreover, there are different areas of study, each with its own concepts of what is significant and what is not. For example, if one molecule in a trillion splits into ions, this is nothing for chemistry, but probably quite a something for atmospheric physics.

As for the question you supposedly intended to ask: no, electrolytic dissociation of dissolved substances never happens in gases the way it happens in water.

Also, welcome to Chem.SE.

You know that compounds can dissociate in solution, for example copper sulphate as a solid , will dissociate in water into copper Cu$^{2+}$ and SO$_4^{2-}$ ions. This occurs because the water can solvate these ions and this turns out to be of lower energy that remaining in the solid. In the gas phase you have to add energy to dissociate a molecule, usually by absorbing a visible or ultra-violet photon. This has to have enough energy to break a bond, for example iodine vapour can be be dissociated with green-blue light ( < approx 500 nm) but a molecule like ozone O$_3$ needs ultra-violet light to break it apart. Dissociation in the gas phase usually produces two radicals such e.g. I$_2$ = I. + I. .