Question

In the following mechanism, which is the rate-determining step?

A.] Step 1: H2(g)+ICl(g)→HI(g)+HCl(g) (slow)
B.] Step 2: HI(g)+ICl(g)→I2(g)+HCl(g) (fast)

Answer 1

The rate-determining step for the provided mechanism is Step 1: H2(g) + ICl(g) → HI(g) + HCl(g), which is labeled as the slow step. This is consistent with the experimental rate law rate = k[ICl][H2], confirming that Step 1's rate law matches the overall reaction's rate law.

Step-by-step explanation:

In the proposed reaction mechanism, the rate-determining step is the slowest step in the sequence of steps that occur during the chemical reaction. According to the information provided:

• Step 1: H2(g) + ICl(g) → HI(g) + HCl(g) (slow)
• Step 2: HI(g) + ICl(g) → I2(g) + HCl(g) (fast)

Since Step 1 is labeled as slow and Step 2 as fast, we can conclude that Step 1 is the rate-determining step. This is consistent with the experimental rate law given as rate = k[ICl] [H2]. Since the rate law for the overall reaction matches the rate law for the slow step, it validates that Step 1 is the rate-determining step. In chemical kinetics, the rate law is determined experimentally and must agree with the rate law for the slowest (rate-determining) step of the reaction mechanism if that step is sufficiently slower than subsequent steps.