How can I calculate the rates and order in the following reaction? #H_2 + Br_2 -> 2HBr#
First and foremost, you need actual data, and second, you need a plausible mechanism. This is the most plausible one, in the presence of heat or light:
Since it overall sums to:
...it works. This is a radical mechanism as you can see.
Now, according to that mechanism, it involves two molecules participating in the two-part rate-determining steps (slow steps), so it is a bimolecular process.
The first two steps are slow because breaking bonds to form radicals is much harder than waiting for two radicals to react (radicals are very reactive). Since the two participants are
Now, let's pretend we actually have data. This is fake data, but let's say it was this:
Each row is one trial.
If we look at rows 1 and 2,
If we look at rows 1 and 3,
So, the rate law can be written as:
which is good enough for high school chemistry.