Hydrofluoric acid is used in the preparation of numerous pharmaceuticals (e.g., Prozac) and industrial materials (e.g., Teflon). It can be produced by the reaction of hydrogen and fluorine gases. Starting with initial concentrations of 2.00 M for H₂ and 2.00 M for F₂, what would be the equilibrium concentration of HF? The equilibrium constant for the reaction K_c = 115.

Question

Quizplus · Accepted Answer

The balanced chemical equation for the reaction is H2 + F2 → 2HF. Let x be the change in concentration of H2 and F2 at equilibrium. At equilibrium, [H2] = [F2] = 2.00 - x, and [HF] = 0 + 2x because 2 moles of HF are produced for each mole of H2 and F2 that react. The equilibrium constant expression is Kc = [HF]^2 / ([H2][F2]). Substituting the given Kc value (115) and the expressions for the equilibrium concentrations gives 115 = (2x)^2 / ((2.00 - x)(2.00 - x)). Solving this equation for x gives x ≈ 1.69. Therefore, the equilibrium concentration of HF = 2x = 2(1.69) = 3.38 M, which is closest to 3.37 M.

Hydrofluoric Acid Is Used in the Preparation of Numerous Pharmaceuticals