Final answer:
The equilibrium constant expression for the reaction CO₂(g) + H₂O(l) ↔ H⁺(aq) + HCO₃⁻(aq) is K = [H⁺][HCO₃⁻] / [CO₂], taking into account only the gaseous and aqueous species, and omitting liquids and solids.
Step-by-step explanation:
The reaction CO₂(g) + H₂O(l) ↔ H⁺(aq) + HCO₃⁻(aq) describes a chemical equilibrium between carbon dioxide, water, and the formation of hydronium ions and bicarbonate ions. To write the equilibrium expression for this reaction, also referred to as the equilibrium constant expression (Keq or K), we only include the concentrations of the gases and aqueous species, not liquids or solids. Therefore, the water molecule being a liquid is not included in the expression. The equilibrium constant expression for this reaction is:
K = [H⁺]+[HCO₃⁻]- / [CO₂]g
Here, the brackets denote the equilibrium concentrations of the species, and only gaseous and aqueous species contribute to the equilibrium concentrations. Liquids and solids are omitted because their concentrations do not change significantly in a reaction. It is essential to note that the concentration of carbon dioxide is expressed in its gaseous form, and water being a liquid does not appear in the expression.