The equilibrium constant for the dissociation of molecular iodine, I₂(𝑔) ⇌ 2 I(𝑔), at 800 K is 𝐾_𝑐 = 3.1×10⁻⁵. (b) Assuming both forward and reverse reactions are elementary reactions, which reaction has the larger rate constant, the forward or the reverse reaction?

Key Concepts

Equilibrium Constant (Kc)

The equilibrium constant, Kc, quantifies the ratio of the concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. For the dissociation of I2, Kc = [I]^2 / [I2]. A small Kc value, like 3.1×10^−5, indicates that at equilibrium, the concentration of reactants (I2) is much greater than that of products (I), suggesting the reaction favors the reactants.

Rate Constants and Reaction Rates

Rate constants (k) are specific to each reaction and temperature, determining the speed of the reaction. The forward reaction rate constant (k_forward) relates to the formation of products, while the reverse reaction rate constant (k_reverse) relates to the formation of reactants. The relationship between Kc and the rate constants is given by Kc = k_forward / k_reverse, which helps in comparing their magnitudes.

Elementary Reactions

Elementary reactions are single-step processes where reactants convert directly to products without intermediates. Each elementary reaction has a specific rate law that reflects its molecularity. In this case, both the forward and reverse reactions are assumed to be elementary, allowing for a straightforward comparison of their rate constants based on the equilibrium constant.