The overall reaction CH₃CHO(g) + I₂(g) → CH₃COI(g) + HI(g) is experimentally found to…
CHEMISTRY · Single correct · AP · Chemistry · Kinetics · Kinetics
Problem
The overall reaction CH₃CHO(g) + I₂(g) → CH₃COI(g) + HI(g) is experimentally found to follow the rate law
rate=k[CH3CHO]
I₂ does not appear in the rate law even though it is a reactant in the balanced equation. Which of the following best accounts for the absence of I₂ in the rate law?
(a) I2 is present in large excess, so its concentration remains effectively constant throughout the reaction.
(b) I2 forms an intermediate in a rapid equilibrium prior to the slow step, allowing its concentration to be expressed in terms of [CH3CHO].
(c) I2 participates only after the rate-determining step, so variations in its concentration do not influence the overall rate.
(d) I2 is regenerated in a later step of the mechanism and therefore cancels out of the rate law.