Chemical Equilibrium

Ch.14

(14-1) Equilibrium

• Reversible rxn in which the forward & reverse rxns occur at = rates

• Amts. of reactants & products are constant

Le Chatelier’s Principle

• If a system at equil. is disturbed the system shifts to relieve the stress

• Inc. T, P, or conc. on 1 side of eq. & rxn is forced in opposite direction

The initial soln color (middle) is a mix of yellow & dark red colors due to the presence of both the Fe+3 & the FeSCN+2 complex.

The addition of Fe+3 causes the soln to turn darker red (left) & the removal of Fe+3 causes the soln to turn yellow (right).

(a) Frozen N2O4 is nearly colorless. (b) As N2O4 is warmed it starts

to dissociate into brown NO2 gas. (c) Eventually the color stops

changing as N2O4(g) & NO2(g) reach conc.’s at which they are

interconverting at the same rate.

(14-2) Equilibrium Constant

• Keq: relates the conc.’s of reactants & products

eq

Equil. Practice

A 1 L vessel contains 1.60 mols NH3, 0.800 mols N2, & 1.20 mols of H2. Calculate Keq.

N2(g) + 3H2(g) 2NH3(g)

1. List known[NH3] = 1.60, [N2] = 0.800, [H2] = 1.20

Equil. Practice

2. Write eq.Keq = _[NH3]2

[N2][H2]3

3. Substitute & solveKeq = (1.60)2 = 1.85

(0.800)(1.20)3

Solubility Product Constant

• Ksp: expression for an ionic solid in equil. w/ its ions in a saturated soln

Ca3(PO4)2(s) 3Ca2+(aq) + 2PO43-(aq)

Ksp = [Ca2+]3[PO43-]2

only aq & g products

Solubility Practice

Calculate the Ksp for a 1.34 x 10-5 M saturated soln of AgCl.

AgCl(s) Ag+(aq) + Cl-(aq)

1. List known1.34 x 10-5 mol AgCl x 1 mol Ag+ = 1.34 x 10-5 mol Ag+

1 mol AgCl

Therefore, [Ag+] = [Cl-] = [AgCl] = 1.34 x 10-5 M

Solubility Practice

2. Write eq.

Ksp = [Ag+][Cl-]

3. Substitute & solveKsp = (1.34 x 10-5 )2

= 1.80 x 10-10

More Solubility Practice

Calculate the Ksp for a 6.54 x 10-5 M saturated soln of Ag2CrO4.

Ag2CrO4(s) 2Ag+(aq) + CrO42-(aq)

Ksp = [Ag+]2[CrO42-]

= [(2)(6.54 x 10-5)]2(6.54 x 10-5)

= 1.2 x 10-12

Common Ion Effect

• Reduction in solubility of an ionic cmpd by the addition of an ion in common w/ it