Consider the equilibrium Na2O(s) + SO2(g) ⇌ Na2SO3(s). (a) Write the equilibrium-constant expression for this reaction in terms of partial pressures. (b) All the compounds in this reaction are soluble in water. Rewrite the equilibrium-constant expression in terms of molarities for the aqueous reaction.

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780137542970

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Step 1: Identify the phases of each compound in the reaction. Na2O is a solid, SO2 is a gas, and Na2SO3 is a solid.

Step 2: Write the equilibrium-constant expression for the reaction in terms of partial pressures. Since solids do not appear in the expression, only the gaseous component, SO2, is included. The expression is K_p = 1/P_{SO2}.

Step 3: Consider the aqueous reaction where all compounds are soluble in water. In this case, all species are in the aqueous phase, and we use molarities to express the equilibrium constant.

Step 4: Write the equilibrium-constant expression for the aqueous reaction in terms of molarities. The expression is K_c = [Na2SO3]/([Na2O][SO2]).

Step 5: Note that in the aqueous expression, the concentration of solids is typically considered constant and thus omitted, simplifying the expression to K_c = 1/[SO2].

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Equilibrium Constant Expression

The equilibrium constant expression quantifies the ratio of the concentrations (or partial pressures) of products to reactants at equilibrium. For gaseous reactions, it is expressed in terms of partial pressures, while for reactions in solution, it is expressed in terms of molarity. The general form is K = [products]^[coefficients] / [reactants]^[coefficients], where square brackets denote concentration or pressure.

Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. This principle helps predict how changes in concentration, pressure, or temperature will affect the position of equilibrium in a chemical reaction.

Solubility and Aqueous Equilibria

Solubility refers to the ability of a substance to dissolve in a solvent, forming a solution. In aqueous equilibria, the concentrations of dissolved species are used to express the equilibrium constant. When all reactants and products are soluble, the equilibrium expression is written in terms of molarity, reflecting the concentrations of the ions or molecules in solution.