A mechanism for the gas-phase reaction H2+I2 ⟶2 HI was discussed in the chapter. (a) Show that t

step 1 A mechanism for the gas phase reaction was discussed in the chapter. We need to show the mechani

A mechanism for the gas-phase reaction H2+I2 ⟶2 HI was...

A mechanism for the gas-phase reaction $$\mathrm{H}_{2}+\mathrm{I}_{2} \longrightarrow 2 \mathrm{HI}$$ was discussed in the chapter. (a) Show that this mechanism predicts the correct rate law, rate $=k\left[\mathrm{H}_{2}\right]\left[\mathrm{I}_{2}\right]$. (fast, equilibrium) (fast, equilibrium) $$\mathrm{H}_{2} \mathrm{I}+\mathrm{I} \longrightarrow 2 \mathrm{HI}$$ (slow (b) Identify any reaction intermediates in this proposed mechanism.

A mechanism for the gas-phase reaction
$$\mathrm{H}_{2}+\mathrm{I}_{2} \longrightarrow 2 \mathrm{HI}$$
was discussed in the chapter. (a) Show that this mechanism predicts the correct rate law, rate $=k\left[\mathrm{H}_{2}\right]\left[\mathrm{I}_{2}\right]$.
(fast, equilibrium) (fast, equilibrium)
$$\mathrm{H}_{2} \mathrm{I}+\mathrm{I} \longrightarrow 2 \mathrm{HI}$$
(slow
(b) Identify any reaction intermediates in this proposed mechanism.

Key Concepts

Reaction Intermediates

Reaction intermediates are species that are formed in one step of a reaction mechanism and then consumed in a subsequent step. They do not appear in the overall balanced equation because their concentrations do not affect the net stoichiometry of the reaction, but they are essential for understanding the stepwise process and kinetics of the reaction.

Pre-equilibrium Approximation

The pre-equilibrium approximation is used when an early step in the mechanism is fast and reversible, establishing equilibrium before the slower, rate-determining step occurs. This allows one to express the concentration of reactive intermediates in terms of the concentrations of the stable reactants, which is crucial for deriving the correct overall rate law.

Rate-Determining Step

The rate-determining step is the slowest step in a reaction mechanism, and it acts as a bottleneck for the overall reaction rate. Since the reaction cannot proceed faster than this slowest step, the overall rate law is determined by this particular step.

Reaction Mechanism

A reaction mechanism explains the step-by-step sequence of elementary reactions by which an overall chemical change occurs. It helps us understand how reactants are converted into products in a multistep process, including the characterization of each step as fast or slow, which in turn determines the overall reaction rate.

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