Control of Reactions

[Racquel Fox 2I]

I am getting really confused on how to tell whether a reaction is controlled by kinetics or thermodynamics. How do you easily tell?

[HilaGelfer_2H]

Hi,

You can tell if a reaction is controlled by kinetics or thermodynamics by seeing if it occurs spontaneously and if it does what is the rate at which it occurs. For instance, in his lectures Dr Lavelle used the conversion of diamond to graphite as an example. Even though this reaction occurs spontaneously (deltaG <0) the energy barrier is so large that this reaction occurs extremely slowly (pretty much not at all since it is so low). Therefore, this reaction is controlled by kinetics.

I hope this helps :)

[LarisaAssadourian2K]

You can easily tell because the kinetic product is the product that is formed faster, while the thermodynamic product is more stable.

[Jacob Schwarz-Discussion 3I]

If a reaction is spontaneous but does not occur due to the presence of a large energy barrier, it is controlled by kinetics. Reversely, if a reaction has a negative delta G and does occur, it is controlled by thermodynamics.