(1)
At equilibrium, the rates of the forward and reverse reactions are equal.
ratef = rater
ratef = K1 [A] [B]
rater = K2 [C] [D]
K1 [A] [B] = K2 [C] [D]
K1
[C] [D]
---- = --------
K2
[A] [B]
K1
---- = Keg
K2
(2) Simply, the ionization (equilibrium) constant is equal to the product of the
mol/L concentrations of the products formed in the reaction divided by the product of the
concentrations of the reactants.
(3)
The equilibrium constant for an acid is called the Ka and for a base the
Kb.
(4) Ka and Kb are determined for weak acids and bases only. If the Ka or Kb
of a strong acid or base, respectively, were determined it would be an infinitely large
number.
(5)
Values of equilibrium constants are interpreted as follows:
(a) The constant indicates the strength of a weak electrolyte.
(b) The smaller the value of the Ka or Kb, the weaker the acid or base
respectively.
9-7.
EXAMPLE
+
What is the [H ] of a 0.100 mol/L solution of acetic acid if the Ka for HC2H3O2 is
1.75 X 10-5?
Solution. Determine the equation for the dissociation of the weak acid.
HC2H3O2 <====> H+ + C2H3O2-
MD0837
9-6