Molar Equilibrium Concentration

The molar equilibrium concentration, or just equilibrium concentration, refers to the molar concentration of a particular species in a solution at equilibrium. To specify the molar equilibrium concentration of a species, it is necessary to know how the solute behaves when it is dissolved in a solvent. For example, the molar equilibrium concentration of H₂SO₄ in a solution with a molar analytical concentration cH₂SO₄ = 1.0 M is actually 0.0 M because the sulfuric acid is completely dissociated into a mixture of H⁺, HSO₄^-, SO₄^-2 ions. There are essentially no H₂SO₄ molecules in this solution. The equilibrium concentrations of the ions are 1.01, 0.99, and 0.01 M, respectively.

Equilibrium molar concentrations are usually symbolized by placing square brackets around the chemical formula for the species. So, for our solution of H₂SO₄ with an analytical concentration of cH₂SO₄ 51.0 M, we write

Example 1

Calculate the analytical and equilibrium molar concentrations of the solute species in an aqueous solution that contains 285 mg of trichloroacetic acid, Cl₃CCOOH (163.4 g/mol), in 10.0 mL (the acid is 73% ionized in water).

Solution

Example 2:

Example 3: