# Reaction mechanism

Write the rate law for the following proposed mechanism for the decomposition of IBr to I2 and Br2.

IBr(g)---------->I(g) + Br(g) (fast)
IBr(g) + Br(g)-------->I(g) + Br2(g) (slow)
I(g) + I(g)--------->I2(g) (fast)

The answer is R=k[IBr]^2. I don't know where this answer comes from. Can anyone please explain it to me step by step? Thank you for your help!

$$rate = k[IBr][Br]$$​
$$rate = k'[IBr]^2$$​