equilibrium constant, or Keq, and (2) the reaction’s equilibrium expression.
For the reaction aA + bB cC + dD, the equilibrium expression is written
as follows:
Keq = (The symbol [ ] means “concentration of,” so [A] means “the concentration of
A.”)
Keep in mind that the concentrations referred to in an equilibrium expression are
those of the species at equilibrium; the coefficients in the balanced equation
become exponents in the equilibrium expression; and only those species whose
concentrations can be varied are included. So, only species that are gaseous or in
solution (and not solids or pure liquids) belong in an equilibrium expression.
Thus, given the reaction
BF 3 (g) + 3H 2 O(l) 3HF(aq) + H 3 BO 3 (aq)(remember that the notation (aq) indicates a species is dissolved in water),
we get the equilibrium expression
Keq = Take a close look at the above equilibrium expression. Notice that the
equilibrium constant Keq is proportional to product concentrations over reactant