If the reaction H2 + Br2 2HBr has a rate law that can be described by k[H2][Br2]1/2, which series of reactions is a possible mechanism for the reaction?
a. Br2 2Br (fast)
Br + H2 HBr + H (slow)
HBr + H + Br → 2HBr (fast)
b. Br2 2Br (slow)
Br + H2 HBr + H (fast)
HBr + H + Br 2HBr (fast)
c.Br2 2Br (slow)
2Br + H2 2HBr (fast)
d. Br2 2Br (fast)
Br + H2 HBr + H (fast)
HBr + H + Br 2HBr (slow)
thanks in advance :)
Nvm, it's A!!
To determine which series of reactions is a possible mechanism for the given reaction, we need to find the rate law of the overall reaction and match it with the rate law expression of the proposed mechanisms.
The rate law for the overall reaction is given as k[H2][Br2]^(1/2).
Let's evaluate each proposed mechanism and compare their rate laws with the overall reaction rate law:
a. Br2 → 2Br (fast)
Br + H2 → HBr + H (slow)
HBr + H + Br → 2HBr (fast)
In the first step, the rate-determining step, the concentration of H2 does not appear, so it cannot be part of the rate law. Therefore, this mechanism does not match the given rate law expression.
b. Br2 → 2Br (slow)
Br + H2 → HBr + H (fast)
HBr + H + Br → 2HBr (fast)
In this mechanism, the rate-determining step is the first step, which involves the decomposition of Br2. The concentration of Br2 is included in the rate law expression, matching the given rate law for the overall reaction. Therefore, this mechanism is a possible one.
c. Br2 → 2Br (slow)
2Br + H2 → 2HBr (fast)
In this mechanism, the rate-determining step does not include the concentration of Br2^(1/2), so it does not match the given rate law expression. Therefore, this mechanism is not possible.
d. Br2 → 2Br (fast)
Br + H2 → HBr + H (fast)
HBr + H + Br → 2HBr (slow)
In this mechanism, the rate-determining step is the last step, which involves the formation of 2HBr. The concentration of HBr is included in the rate law expression, but the concentrations of H and Br are not. Therefore, this mechanism does not match the given rate law expression.
Based on the comparison of the rate laws, the correct answer is option b. Br2 → 2Br (slow), Br + H2 → HBr + H (fast), and HBr + H + Br → 2HBr (fast)