CHEMISTRY · Single correct · AP · Chemistry · Kinetics · Kinetics
Problem
The overall reaction Br2+2H2O→2HBr+H2O2 is being investigated. A student suggests the following three-step mechanism.
1. Br2+H2O→HBr+HOBr
2. HOBr+H2O→HBrO2+H+
3. HBrO2+H+→HBr+H2O2
Which of the following best explains why this mechanism cannot be correct?
(a) The proposed mechanism produces a rate law of rate=k[Br2][H2O], which conflicts with the experimentally observed rate law for the reaction.
(b) In one step three species would have to collide simultaneously, an event that is statistically unlikely for an elementary process.
(c) Charge is not conserved in one of the proposed elementary steps, violating the principle of charge conservation.
(d) Adding the three steps results in three bromine atoms in the products but only two in the reactants, so the mechanism cannot be stoichiometrically correct.