At 500 K, the equilibrium constant for the dissociation reaction H2(g) ⇌ 2H(g) is very small (Kc = 1.2 × 10⁻⁴²). (a) What is the molar concentration of H atoms at equilibrium if the equilibrium concentration of H2 is 0.10 M? (b) How many H atoms and H2 molecules are present in 1.0 L of 0.10 M H2 at 500 K?

The equilibrium constant (Kc) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. A small Kc value, like 1.2 × 10⁻⁴², indicates that the reaction favors the reactants (H2) over the products (H atoms), suggesting that at equilibrium, the concentration of H atoms will be very low compared to H2.

A dissociation reaction involves the breaking apart of a compound into its constituent elements or simpler compounds. In this case, H2(g) dissociates into 2H(g). Understanding this reaction is crucial for calculating the concentrations of H atoms at equilibrium, as it directly relates to how the initial concentration of H2 influences the formation of H atoms.

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. In this scenario, the stoichiometric coefficients indicate that one mole of H2 produces two moles of H atoms. This relationship is essential for determining the molar concentrations of H atoms and H2 in the system, allowing for accurate calculations of their quantities at equilibrium.