Rate determining step is slo
so rate = k[H2]^2
However I is the intermediate and rate law is always in terms of reactant of the overall reaction.
S we need to replace intermediate by the reactant from the fast equilbrium step which is I₂
 rate = k[H2][I₂]

Key Concept (AP Chemistry level)
Intermediates (like
𝐼
I) must be eliminated.
Use equilibrium expression of fast step to substitute.
Final rate law must contain only reactants from overall reaction.

I am also confused about how to draw a energy diagram of a reverse uncatalyzed rxn?

Hi Uma Mam!

I am also confused about how to draw a energy diagram of a reverse uncatalyzed rxn?

Here is the problem that I am specifically stuck on. 

Hi Mam!

I was wondering could you explain how to substitute a intermediate to find a rate law again?