Question

For each reaction mechanism, identify the rate-determining step?

1) Step 1: no(g) + Cl₂(g) → noCl₂(g) (fast)
2) Step 2: noCl₂(g) → no(g) + 2nocl(g) (slow)
3) Step 1: H₂O₂(aq) + i-(aq) → hoi(aq) + oh -(aq) (slow)
4) Step 2: hoi(aq) + i -(aq) → i2(aq) + oh -(aq) (fast)

Answer 1

The rate-determining step in a reaction mechanism is the slowest step. For the cases provided, it is explicitly indicated which steps are slow and hence rate-determining. The overall reaction rates and mechanisms are derived considering these rate-determining steps.

Step-by-step explanation:

To identify the rate-determining step in a reaction mechanism, we look for the slowest step since it controls the overall reaction rate. For the given mechanisms:

• Step 1: NO(g) + Cl₂(g) → NOCl₂(g) (fast)
• Step 2: NOCl₂(g) → NO(g) + 2NOCl(g) (slow)

Here, the rate-determining step is Step 2, as it is labeled slow.

For the reaction mechanism involving three steps:

1. Step 1: NO + NO = N₂O₂
2. Step 2: N₂O₂ + H₂ = H₂O + N₂O
3. Step 3: N₂O + H₂ = N₂ + H₂O

The rate-determining step could be identified by matching the rate law of a slow step with the experimentally determined rate law for the overall reaction.

For the phosgene formation:

• Cl₂ (g) = 2Cl(g) (fast)
• CO(g) + Cl(g) —— COCl(g) (slow)
• COCl(g) + Cl(g) —— COCl₂ (g) (fast)

The overall reaction is CO(g) + Cl₂(g) → COCl₂(g).

Finally, using the mechanism:

• Step 1: NO(g) + Cl₂ (g) ⇒ NOCl₂ (g) fast
• Step 2: NOCl₂ (g) + NO(g) —— 2NOCl(g) slow

The rate law for the overall reaction would be derived using the slow step, leading to a rate law of rate = k₂[NOCl₂][NO], after considering that NOCl₂ is in steady-state concentration.