[Diamonds]

Given a reaction profile such as http://duch.sd57.bc.ca/~rmcleod/Chemists_Corner/PE_Diagram_Multi_files/COplusCl2_ver_1-640.gif

Is the rate-determing step the one that has the highest E_a relative to the one before it, or is it the one that has the highest E_a from the reactants? In this example, it doesn't matter but say you had

A is the reactant, and it is at 50 kJ. B is an intermediate, and its position on the diagram is 150 kJ. C is another intermediate at 200 kJ, and the product D is at 25 kJ.

So then which step is rate-determining? A to B or B to C? Because the reaction from A to B is 100 kJ difference, which is bigger than the other two, but do you compare it from the reactant, A, or the previous equation?

[Sunil Simha]

Actually, rather than the difference in the energy of the reactant and product (or intermediate), the activation energy for that step plays a greater role in determining the RDS. So... which step do you think will be the RDS in a given reaction?