Predict whether a molecule will decay due to heat.

[Tiiba]

I'm trying to understand the chemistry of stars. At what point do molecules really end?

I guess there would be no one temperature where every molecule of hydrogen breaks apart in unison, but there should be an equation that says: if a diatomic gas is held together by 100 kJ/mol, at a temperature of 5000 kelvin it will be mostly individual atoms.

So, is there? I can't find anything.

(And if it's a complex situation for real gases, is there a formula that would make the same prediction for two hard spheres held together by a rubber band, or some other idealization?)

 

[Ygggdrasil]

You could calculate the Boltzmann factor to figure out the ratio of bound and unbound hydrogen atoms. (Though, this calculation would be imperfect as it would ignore the effect of entropy)

 

[Kevin McHugh]

You can look up bond dissociation temperatures for all kinds of bonds. Then you can calculate the temperature required to break those bonds.