Question

Write the equation and mechanism of the theoretically fastest reaction that should have occurred. The equation should be written with starting materials on one side and product on the other, and the mechanism should have the species with arrows depicting movement of electrons with intermediates showing (where applicable). Use actual alkyl halide and reagent.

Answer 1

A two-step mechanism consistent with the rate law rate = k[IC1] [H₂] for a reaction between IC1 and H₂ can be established with HI as the intermediate, and the slow step being the rate-determining step.

Step-by-step explanation:

Writing a Mechanism for the Fastest Reaction

The question asks to write the equation and mechanism of a fast chemical reaction using actual reactants and products. The provided example is a reaction between an alkyl halide, IC1, and hydrogen gas, which produces HCl and iodine as a solid. Considering the rate law is given as rate = k[IC1] [H₂], we can propose a two-step mechanism involving bimolecular elementary reactions. HI is indicated as an intermediate in the provided hint.

Here is a suggested mechanism that is consistent with the experimentally determined rate law:

• Step 1 (fast): IC1 + H₂ → HI + HCl (rate law: rate = k1[IC1][H₂])
• Step 2 (slow): HI + IC1 → HCl + I₂ (rate law: rate = k2[HI][IC1])

In this mechanism, Step 2 is the rate-determining step (slow step) because it has a higher activation energy and will control the rate of the overall reaction. The rate for the overall reaction can be expressed in terms of reactants by assuming that equilibrium is quickly established in Step 1 and, therefore, the intermediate, HI, can be expressed in terms of IC1 and H₂ which is consistent with the given rate law.

To explain the concept of a rate-determining step, it's the slowest step in a sequential reaction that determines the reaction rate, analogous to the narrowest part of a funnel through which the entire flow must pass.