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Temperature and state

This is a bit of a random question but it occurred to me so let's ask:

Let's say we have a sample of a large molecule or an amino acid or something (not relevant for our discussion). And then we raise the temperature in which this sample is held. And then keep raising it. Eventually we will end up with nuclei and electrons floating around.

In what order does this happen? i.e. do the bonds between the atoms break, then the ionizations begin? Or are the electrons removed first?

Reply 1

charco

Study Forum Helper

Original post by Big-Daddy

Logically the least energy demanding process should occur first. Bond enthalpy terms are usually of the order of 200 - 600 kJmol^-1 (ish). A C-H bond is (on average) 412 kJ mol^-1.

Ionisation energies for atoms usually higher (obviously it depends on the element), but as you don't have individual atoms you would need to think about molecular orbitals and the promotion /ionisation of electrons there.

A real life example would be the mass spectrometer. In this the molecules are ionised first and then the ions fragment. However, this isn't with thermal energy, rather with a beam of high energy electrons.

However, it seems likely to me that you would first get ionisation of the molecule and/or fragmentation, depending on the species under consideration.