Learning Goals

• identify common equilibrium constants, including Keq, Ksp, Kw, Ka, Kb and write the expressions for each

• solve problems related to equilibrium by performing calculations involving concentrations of reactants and products

Equilibrium Law

• mathematical description of chemical system at equilibrium

• defined by the equilibrium constant, K• Complete Inv. 7.2.1 on p. 473-474

Writing Equilibrium Law EquationsFor aA + bB cC + dD,

K = [C]c[D]d (omit units) [A]a[B]b

• omit (s) and (l)

• include only (aq) and (g)

Ex. H2(g) + S(l) H2S(g)

Ex. NH3(g) + H2O(l) NH4+

(aq) + OH-(aq)

p. 431 #1-3, p. 434 #1

Calculating K

• Write the equilibrium law equation.• Substitute [ ]eq

• K can be used to predict the equilibrium position (Review Equilibrium Position table in lesson 1 and add a column for K.)

• Sample Problem 2 (p. 430)

In a closed vessel at 500°C, N2(g) + 3 H2(g) 2 NH3(g)

The equil. conc. of N2, H2 and NH3, respectively, are 1.50 x 10-5 M, 3.45 x 10-1 M and 2.00 x 10-4 M. Calculate K.

• Sample Problem 3 (p. 431)

In a closed vessel at 500°C, 2 NH3(g) N2(g) + 3 H2(g)

The equil. conc. of N2, H2 and NH3, respectively, are 1.50 x 10-5 M, 3.45 x 10-1 M and 2.00 x 10-4 M. Calculate K.

K (synthesis of ammonia)K’ (decomposition of ammonia)Mathematical relationship b/w K and K’?

K = 1/K’

What does the magnitude of K tell us about the equilibrium position?

A. In a closed system at 25°C,2 CO(g) + O2(g) 2 CO2(g) K = 3.3 x 1091

B. Decomposition of water at 1000°C,2 H2O(g) 2 H2(g) + O2(g) K = 7.3 x 10-10

C. NO2(g) + NO(g) N2O(g) + O2(g) K = 0.951

Homework

• p. 436 #1-6