Solution: Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g)The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms.Proposed mechanism I:

Consider the gas-phase reaction: H₂(g) + I₂(g) → 2 HI(g)
The reaction was experimentally determined to be first order in H₂ and first order in I₂. Consider the proposed mechanisms.
Proposed mechanism I: H₂(g) + I₂(g) → 2 HI(g) Single step
Proposed mechanism II:
I₂(g) → 2 I(g)          Fast
H₂(g) + 2 I(g) → 2 HI(g)          Slow

What kind of experimental evidence might lead you to favor mechanism II over mechanism I?