Unit 7: Topic 7 - Calculating Equilibrium Concentrations Flashcards
The reaction HF(aq) + H2O (l) ⇌ F- (aq) + H3O+ (aq) has a K = 6.6 * 10^-4. The initial concentration of HF is [HF]0 = 0.150M. When this reaction reaches equilibrium, what is the concentration of [H3O+]?
The strategy here is an ICE table, as shown here. Notice that H2O has been omitted from the ICE table since it is a liquid and is not present in the calculation of K. The acronym for ICE is Initial, Change, and Equilibrium (sometimes RICE is used, R for reaction). In the Initial row, we list the initial concentrations of the reactants and products present in K: HF has an initial concentration of 0.150M, whereas F- and H3O+ have initial concentrations of 0M. In the Change row, we list our changes proportional to a variable “x.” Since reactants form products, this value “x” is negative for reactants and positive for products. All coefficients are one, so each change is either -x or +x (if a product had coefficient 2, the change would be +2x; if a reactant had coefficient 3, the change would be -3x, etc.). The Equilibrium row is simply the sum of the initial and change rows. Now, we can solve for [H3O+] = x. Use a calculator (graphically or quadratic formula) to solve: x = 0.00963M.
