Slide 1 ___________________________________ 16 Chemical Equilibrium
___________________________________ ___________________________________ ___________________________________ ___________________________________ Keeping fish in an aquarium requires
maintaining an equilibrium among the
living organisms and the water.
___________________________________ Foundations of College Chemistry, 14th Ed.
___________________________________ Morris Hein and Susan Arena
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 16.1
Rates of Reaction
16.2
Chemical Equilibrium
16.3
Le Châtelier’s Principle
16.4
Equilibrium Constants
16.5
Ion Product Constant for Water
16.6
Ionization Constants
16.7
Solubility Product Constant
16.8
Buffer Solutions: The Control of pH
© 2014 John Wiley & Sons, Inc. All rights reserved.
3 ___________________________________ Chapter Outline
2 Slide ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Rates of Reaction
___________________________________ Chemical Kinetics:
study of reaction rates and reaction mechanisms.
___________________________________ Factors That Affect Reaction Rates
___________________________________ ___________________________________ 1. Frequency of collisions between reactants
(concentration effects).
2. Energy needed for effective collisions between
reactants to produce products (temperature and
catalytic effects).
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ Slide ___________________________________ Reversible Reactions
4 ___________________________________ Most chemical reactions are reversible, consisting of
a forward reaction (where reactants are converted to
products) and a reverse reaction (where products
are converted back to reactants).
(forward reaction)
A+B
C+D
(reverse reaction)
C+D
A+B
___________________________________ ___________________________________ ___________________________________ Eventually, the rate of the forward reaction is equal
to the rate of the reverse reaction.
This point is when equilibrium is attained.
A+B
___________________________________ C+D
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Reversible Reactions
5 ___________________________________ Equilibrium vapor pressures are measured at different
temperatures to generate vapor pressure curves.
liquid + heat
___________________________________ vapor (evaporation)
Forward Reaction: liquid + heat
Reverse Reaction: vapor
___________________________________ vapor
liquid + heat (condensation)
___________________________________ At equilibrium:
Rate of evaporation = Rate of condensation
___________________________________ At this point, the vapor pressure of the liquid
does not change with time.
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Reversible Reactions
6 2 NO2 (g)
Brown gas
Colorless gas
Forward Reaction:
2 NO2 (g)
Reverse Reaction:
N2O4 (g) + heat
25 °C
___________________________________ N2O4 (g) + heat
___________________________________ N2O4 (g) + heat
2 NO2 (g)
___________________________________ 90 °C
___________________________________ Reversible reaction of
NO2 and N2O4.
More dark brown NO2
molecules are present
at higher temperature.
___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 7 ___________________________________ Rates of Reactions and Equilibrium
___________________________________ The rate of the forward reaction (red) and back reaction
(blue) become equal at equilibrium (purple).
___________________________________ The forward reaction rate decreases
as reactants are consumed to form products.
___________________________________ ___________________________________ ___________________________________ The reverse reaction rate starts at 0
(no product is present to react at this time)
and increases as the amount of product increases.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Chemical Equilibrium
8 ___________________________________ Chemical Equilibrium: a dynamic state in which two
opposing processes (forward and reverse reactions)
occur simultaneously at the same rate.
___________________________________ When chemical equilibrium is achieved:
___________________________________ Rateforward reaction = Ratereverse reaction
Example
___________________________________ HF (aq) + H2O (l)
H3
O+
(aq) +
F–
(aq)
___________________________________ At equilibrium, HF is ionizing at the same rate that
the acid is reforming, so the concentrations of HF,
H3O+ and F– remain constant.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 9 ___________________________________ ___________________________________ Chemical Equilibrium Practice
___________________________________ Equilibrium is achieved in a chemical reaction when:
___________________________________ a. Reactants are completely consumed.
___________________________________ b. The concentrations of all reactants and products
___________________________________ become equal.
c. The rates of the opposing reactions become equal.
___________________________________ d. The forward and reverse reactions stop.
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 10 ___________________________________ Le Châtelier’s Principle
___________________________________ Le Châtlelier’s principle: if a stress is applied to a system,
___________________________________ the system will respond to relieve that stress and
restore equilibrium under the new set of conditions.
___________________________________ Common Stressors of Chemical Equilibria
___________________________________ 1. Changes in concentration
2. Temperature changes
3. Changes in gas volume
___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 11 ___________________________________ Effect of Concentration
___________________________________ For the reaction:
3 H2 (g) + N2 (g)
2 NH3 (g)
___________________________________ At equilibrium:
Rateforward reaction = Ratereverse reaction
___________________________________ If H2 is added to the reaction at equilibrium,
the forward rate would be increased, producing
more NH3 and consuming additional H2 and N2.
As the amount of NH3 increases,
the rate of the forward reaction will decrease while
the reverse reaction rate increases (see Slide 16-7).
Eventually, the two rates become equal again
and equilibrium is achieved.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 12 ___________________________________ ___________________________________ ___________________________________ ___________________________________ Adding Reactant to a System
at Equilibrium
___________________________________ For the reaction:
3 H2 (g) + N2 (g)
___________________________________ 2 NH3 (g)
If H2 is added to the reaction at equilibrium,
more NH3 is produced.
The equilibrium is said to have shifted to the right.
___________________________________ Summary of H2 Addition to the System
___________________________________ Compound
Change in Reagent
Concentration
H2
decreases
N2
decreases
NH3
increases
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ Slide 13 ___________________________________ Adding Reactant to a System
at Equilibrium
___________________________________ For the generic reaction:
Reactant
___________________________________ Product
The following table summarizes effects of
added/removed reagents on the equilibrium.
Compound
Shift
Add reactant
Right
Product
Reactant
Remove reactant
Left
Reactant
Product
Add product
Left
Reactant
Product
Remove product
Right
Product
Reactant
Increase in
Decrease in
equilibrium
equilibrium
concentration concentration
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Effect of Concentration
14 Cu2+
___________________________________ For the reaction:
(aq) + 4 NH3 (aq)
[Cu(NH3)42+] (aq)
Pale blue
Royal blue
___________________________________ What color will be observed if ammonia is
added to an equilibrium mixture?
Ammonia will shift the reaction to the right,
resulting in a royal blue color.
___________________________________ ___________________________________ Summary of NH3 Addition to the System
Compound
Change in Reagent
Concentration
Cu2+
decreases
NH3
decreases
NH3
increases
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 15 ___________________________________ ___________________________________ ___________________________________ Effect of Concentration
For the reaction:
CH3COOH (aq) + H2O (l)
CH3COO- (aq) + H3O+ (aq)
___________________________________ Adding CH3COO- to the equilibrium mixture will:
___________________________________ 1. Decrease the concentration of CH3COO-.
2. Cause an increase in the rate of the reverse reaction,
shifting the reaction to the left.
3. Decrease the H3O+, increasing the pH.
___________________________________ ___________________________________ Effect of added CH3COO- concentration on observed pH
___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 16 ___________________________________ Effect of Concentration
For the reaction:
CH3COOH (aq) + H2O (l)
CH3COO- (aq) + H3O+ (aq)
___________________________________ Adding NaOH to the equilibrium mixture will:
___________________________________ 1. Decrease the H3
as the hydronium ion would react
with the hydroxide ion.
2. Would cause a decrease in the reverse reaction rate,
causing the reaction to shift towards the right.
O+,
___________________________________ ___________________________________ Summary of NaOH Addition to the System
Compound
CH3COOH
H3O+
Change in Concentration
decreases
decreases
CH3COO-
increases
17 ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Effect of Concentration Practice
___________________________________ For the reaction:
3 H2 (g) + N2 (g)
2 NH3 (g)
___________________________________ In which direction will the equilibrium shift when
the concentration of nitrogen is increased?
a. Shift to the right
b. Shift to the left
Compound
Change in Reagent
Concentration
H2
decreases
N2
decreases
NH3
increases
c. No shift will occur
18 ___________________________________ ___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Summary of N2 Addition
to the System
___________________________________ Effect of Concentration Practice
___________________________________ For the reaction:
AgCl (s)
Ag+ (aq) + Cl- (aq)
___________________________________ In which direction will the equilibrium shift when
the concentration of chloride ion is increased?
a. Shift to the right
b. Shift to the left
c. No shift will occur
___________________________________ Summary of Cl- Addition
to the System
Compound
Change in Reagent
Concentration
AgCl
increases
Ag+
decreases
Cl-
decreases
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ ___________________________________ Slide 19 ___________________________________ Effect of Concentration Practice
___________________________________ For the reaction:
2+
Cu (aq) + 4 NH3 (aq)
[Cu(NH3)42+] (aq)
Pale blue
___________________________________ Royal blue
What color will the reaction be if HCl is added,
which will react with the ammonia?
a. Pale blue
b. Royal blue
c. No color change
Compound
Change in Reagent
Concentration
NH3
increases
Cu2+
increases
Cu(NH3)42+
decreases
20 ___________________________________ ___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Summary of HCl Addition
to the System
___________________________________ Effect of Concentration Practice
___________________________________ For the reaction:
H2 (g) + I2 (g)
2 HI (g)
___________________________________ If I2 (g) is added to the equilibrium mixture,
the concentration of H2 will:
a. Increase
b. Decrease
c. Not change
Compound
Change in Reagent
Concentration
H2
decreases
I2
increases
HI
increases
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 21 ___________________________________ Summary of I2 Addition
to the System
___________________________________ ___________________________________ ___________________________________ ___________________________________ Effect of Changes in Volume
___________________________________ A decrease in volume in a gas phase reaction will increase
the pressure of all gases (both reactants and products).
___________________________________ The balanced equation determines whether the change
___________________________________ in volume will cause a shift to the left or right.
___________________________________ The reaction will shift to the side with the smaller number
of gas molecules when the volume is decreased.
___________________________________ The reaction will shift to the side with the larger number
___________________________________ of gas molecules when the volume is increased.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 22 ___________________________________ Effect of Changes in Volume
___________________________________ For the reaction:
3 H2 (g) + N2 (g)
2 NH3 (g)
4 moles of gas
2 moles of gas
How will a decrease in the volume of the container
affect the equilibrium concentrations?
The equilibrium will shift to the right,
producing more ammonia.
___________________________________ ___________________________________ ___________________________________ Summary of Volume Change in the System
Compound Change in Reagent Concentration
H2
decreases
N2
decreases
NH3
increases
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 23 ___________________________________ ___________________________________ Effect of Changes in Volume
___________________________________ For the reaction:
___________________________________ H2 (g) + I2 (g)
2 HI (g)
2 moles of gas
2 moles of gas
___________________________________ ___________________________________ The equilibrium will remain unchanged,
as the number of gas molecules is the same
on both sides of the chemical equation.
24 ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Effect of Volume Practice
___________________________________ For the reaction:
PCl5 (g)
PCl3 (g) + Cl2 (g)
1 mole of gas
2 moles of gas
___________________________________ In which direction will the equilibrium shift when
the volume of the reaction vessel is decreased?
a. Shift to the right
Summary of Volume Decrease
b. Shift to the left
Compound
c. No change occurs
___________________________________ ___________________________________ Change in Reagent
Concentration
PCl5
increases
PCl3
decreases
Cl2
decreases
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ Slide 25 ___________________________________ Effect of Volume Practice
___________________________________ For the reaction:
2 CO2 (g)
2 CO (g) + O2 (g)
2 moles of gas
___________________________________ 3 moles of gas
In which direction will the equilibrium shift when
the volume of the reaction vessel is increased?
a. Shift to the right
Summary of Volume Increase
b. Shift to the left
Compound
Change in Reagent
Concentration
CO2
decreases
c. No change occurs
CO
increases
O2
increases
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 26 ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Effect of Volume Practice
___________________________________ For the reaction:
AgCl (s)
Ag+ (aq) + Cl- (aq)
0 moles of gas
0 moles of gas
___________________________________ In which direction will the equilibrium shift when
the volume of the reaction vessel is decreased?
___________________________________ a. Shift to the right
___________________________________ b. Shift to the left
___________________________________ c. No change occurs
Remember, pressure and volume changes only
affect reactions involving gases!
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 27 ___________________________________ ___________________________________ Effect of Temperature
___________________________________ An increase in temperature increases both the rates of
the forward and reverse reactions because of the
increase in kinetic energy of all collisions in the system.
___________________________________ The application of heat to increase the temperature
favors a reaction where heat is a reactant
(i.e. heat is absorbed). When heat is absorbed,
the reaction is called endothermic.
___________________________________ ___________________________________ A + heat
B
When heat is given off, the reaction is called exothermic.
A
B + heat
Treat heat as any other reactant or product in a
Le Châtelier problem to predict effects on equilibrium!
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ Slide ___________________________________ Effect of Temperature
28 ___________________________________ For the reaction:
2 NO2 (g)
Brown gas
N2O4 (g) + heat
___________________________________ Colorless gas
Increasing the reaction temperature favors the
reverse reaction, shifting the equilibrium to the
left towards the brown gas.
25°C
___________________________________ ___________________________________ 90°C
Reversible reaction of NO2
and N2O4.
More dark brown NO2
molecules are
present at higher
temperature.
29 ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Effect of Temperature
___________________________________ For the reaction:
3 H2 (g) + N2 (g)
How will an increase in temperature affect the
equilibrium concentration of ammonia?
___________________________________ 1. The reaction is exothermic (heat is evolved).
2. Increasing the temperature adds heat to the system.
3. The reverse reaction is favored and the equilibrium will
shift to the left.
4. The amount of ammonia will then decrease.
___________________________________ 30 ___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ 2 NH3 (g) + heat
___________________________________ Effect of Temperature Practice
___________________________________ For the reaction:
PCl5 (g) + heat
PCl3 (g) + Cl2 (g)
___________________________________ In which direction will the equilibrium shift when
the reaction is cooled?
a. Shift to the right
Summary of Temperature Decrease
b. Shift to the left
Compound
Change in Reagent
Concentration
PCl5
increases
PCl3
decreases
Cl2
decreases
c. No change occurs
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 31 ___________________________________ Effect of Catalysts
___________________________________ Catalyst: substance that increases the rate of a
chemical reaction but that can be fully recovered
at the end of the reaction.
___________________________________ ___________________________________ A catalyst does not shift the equilibrium
of a chemical reaction.
___________________________________ A catalyst lowers the activation energy of a reaction,
affecting only the rate of reaction.
___________________________________ Activation energy: minimum energy required
for a chemical reaction to occur.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 32 ___________________________________ ___________________________________ Reaction Coordinate Diagram
___________________________________ Energy Diagram for an Exothermic Reaction
___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 33 ___________________________________ Effect of Catalyst Practice
___________________________________ For the reaction:
3 H2 (g) + N2 (g)
2 NH3 (g) + heat
___________________________________ In which direction will the equilibrium shift
when a catalyst is added?
___________________________________ a. Shift to the right
___________________________________ b. Shift to the left
c. No change occurs
___________________________________ Catalysts only affect the rate of reaction,
not the chemical equilibrium!
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ Slide 34 ___________________________________ Equilibrium Constants
___________________________________ For the equilibrium:
aA+bB
cC+dD
___________________________________ There is a mass law expression defined as
the equilibrium constant (Keq):
Equilibrium constant = Keq =
___________________________________ [C]c[D]d
[A]a[B]b
___________________________________ Only substances which possess molar concentrations that
___________________________________ vary will appear in the equilibrium constant expression.
Gases and aqueous solutions are the only substances that
___________________________________ typically appear in equilibrium constant expressions.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 35 ___________________________________ Equilibrium Constants
___________________________________ For the equilibrium:
3 H2 (g) + N2 (g)
___________________________________ 2 NH3 (g)
___________________________________ The equilibrium constant can be written as:
Keq =
[NH3]2
[H2]3[N2]
___________________________________ ___________________________________ The value of Keq is determined by the concentrations
of both the reactants and products.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 36 ___________________________________ ___________________________________ Equilibrium Constants
___________________________________ The magnitude of an equilibrium constant indicates
the extent of a chemical reaction.
___________________________________ Keq >> 1 indicates the relative amounts of products
___________________________________ are favored when compared to the reactants.
___________________________________ Keq << 1 indicates the relative amounts of reactants
are favored when compared to the products.
___________________________________ Keq ~ 1 means that both reactants and products
are present in significant amounts.
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ Slide ___________________________________ Equilibrium Constants
37 ___________________________________ Calculate Keq for the following reaction:
PCl5 (g)
___________________________________ PCl3 (g) + Cl2 (g)
___________________________________ when [PCl5] = 0.030 M, [PCl3] = 0.97 M and [Cl2] = 0.97 M.
Keq =
[PCl3][Cl2]
[PCl5]
=
(0.97)(0.97)
0.030
___________________________________ ___________________________________ = 31
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 38 ___________________________________ Equilibrium Constants Practice
___________________________________ Calculate Keq for the following reaction:
H2 (g) + I2 (g)
___________________________________ 2 HI (g)
when [H2] = 0.228 M, [I2] = 0.228 M and [HI] = 1.544 M.
___________________________________ a. 29.7
___________________________________ b. 59.4
c. 0.0337
d. 0.0219
Keq =
[HI]2
[H2][I2]
=
(1.544)2
(0.228)(0.228)
= 45.9
___________________________________ e. 45.9
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 39 ___________________________________ Ion Product Constant for Water
___________________________________ Pure water auto(self) ionizes
___________________________________ H2O (l) + H2O (l)
H3O+ (aq) + OH- (aq)
[H3O+] = [OH-] = 1.00 x 10-7 M
___________________________________ Realize any water solution contains both H3O+ and OH-.
___________________________________ Ion Product Constant for Water
___________________________________ Kw = [H3O+][OH-] = 1.00 x 10-14
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ Slide 40 Relationship Between [H3O+] and [OH–]
___________________________________ Ion Product Constant for Water
Kw = [H3O+][OH-] = 1.00 x 10-14
___________________________________ pH and pOH
___________________________________ pH = -log[H3O+]
pOH = -log[OH-]
___________________________________ Relationship Between pH and pOH
pH + pOH = 14
___________________________________ Relationship Between [H3O+] and [OH-] and pH/pOH
___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Using Kw and pH Practice
41 ___________________________________ What is the [H3
O+]
in a 0.0152 M solution of NaOH?
___________________________________ Kw = [H3O+][OH-] = 1.00 x 10-14
[H3O+] = 1.00 x 10-14/[OH-]
___________________________________ = 1 x 10-14/0.0152 = 6.58 x 10-13 M
___________________________________ Calculate the pH of a 0.0152 NaOH solution.
___________________________________ pH =- log[H3O+]
= -log(6.58 x 10-13) = 12.182
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Using Kw and pH Practice
42 ___________________________________ What is the [OH-] in a 0.00010 M solution of HCl?
a.
b.
c.
d.
1 x 10-14 M
1 x 10-10 M
1 x 10-4 M
1 x 10-7 M
Kw = [H3O+][OH-] = 1.00 x 10-14
[OH-]
10-14/[H
___________________________________ O+]
= 1.00 x
3
= 1 x 10-14/0.0001
= 1.00 x 10-10 M
___________________________________ ___________________________________ What is the pOH of a 0.00010 M solution of HCl?
a.
b.
c.
d.
1
4
10
13
___________________________________ pOH = -log[OH-]
= -log(1.00 x 10-10) = 10.0
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 43 ___________________________________ Ionization Constants
___________________________________ Acid Ionization Constant (Ka): a measure of the
extent to which a weak acid ionizes in water.
___________________________________ For a general weak acid (HA):
HA (aq) + H2O (l)
H3O+ (aq) + A- (aq)
___________________________________ [H3O+][A-]
Ka =
[HA]
___________________________________ Water is the solvent. Because its concentration does
not change measurably during the ionization,
___________________________________ water is not included in the Ka expression.
The larger the value of Ka, the more significant the
___________________________________ ionization, the stronger the acid.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 44 ___________________________________ Calculating [H3O+] in a Weak Acid
___________________________________ Determine the [H3O+] of a 0.20 M solution of CH3COOH.
Ka = 1.8 x 10-5
Equation
CH3COOH + H2O
Initial (M)
Change (M)
Equilibrium (M)
Ka =
___________________________________ CH3
0.2
-x
0.2 - x
COO-
+ H3
0
+x
x
[CH3COO-][H3O+]
[CH3COOH]
x2 = (0.20 - x)(1.8 x 10-5)
=
x2
0.20 - x
O+
___________________________________ 0
+x
x
___________________________________ = 1.8 x 10-5
___________________________________ x2 = 3.6 x 10-6 - 1.8 x 10-5x
___________________________________ x = [H3O+] = 1.90 x 10-3 M
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 45 ___________________________________ % Ionization of a Weak Acid
___________________________________ Determine the % ionization of a
0.20 M CH3COOH solution.
CH3COOH (aq) + H2O (l)
% ionization =
CH3COO- (aq) + H3O+ (aq)
[H3O+]
initial acid concentration
% ionization =
___________________________________ 1.9 x 10-3
0.20
___________________________________ ___________________________________ x 100 %
___________________________________ x 100% = 95%
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ Slide 46 ___________________________________ Calculating [H3O+] in a Weak Acid
___________________________________ Determine the [H3O+] of a 0.10 M solution of HCN.
Ka = 4.0 x 10-10
Equation
HCN + H2O
___________________________________ CN- + H3O+
Initial (M)
0.10
Change (M)
-x
Equilibrium (M) 0.10 - x
0
+x
x
[CN-][H3O+]
Ka =
=
[HCN]
x2 = (0.10 - x)(4.0 x 10-10)
x2
0.10 - x
___________________________________ 0
+x
x
___________________________________ = 4.0 x 10-10
___________________________________ x2 = 4.0 x 10-11 - 4.0 x 10-10x
___________________________________ x = [H3O+] = 6.3 x 10-6 M
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Solubility Product Constants
47 ___________________________________ Saturated solutions have solid in equilibrium
___________________________________ with dissolved solute.
AxBy (s)
x Ay+ (aq) + y Bx- (aq)
___________________________________ The solubility product (Ksp) is defined as:
Ksp =
___________________________________ [Ay+]x[Bx-]y
___________________________________ The amount of solid does not affect the equilibrium
and is not included in the equilibrium expression.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Solubility Product Practice
48 ___________________________________ Calculate the solubility (x), [Hg2+] ,
and
[Br-]
of HgBr2 if Ksp = 1.3 x
10-19.
___________________________________ Ksp = [Hg2+][Br-]2 = 1.3 x 10-19
Equation
HgBr2 (s)
Initial (M)
Change (M)
Equil. (M)
___________________________________ Hg2+ (aq) + 2 Br- (aq)
0
+x
x
0
+2x
2x
___________________________________ ___________________________________ Ksp= x(2x)2 = 4x3
x = solubility = [Hg2+] = 3.2 x 10-7 M
___________________________________ [Br-] = 2x = 6.4 x 10-7 M
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Solubility Product Practice
49 ___________________________________ The Ksp of AgI is 8.3 x 10-17. What is the solubility of AgI?
Equation
AgI (s)
Ag+ (aq) + I- (aq)
Initial (M)
Change (M)
Equil. (M)
0
+x
x
a. 8.3 x 10-17
0
+x
x
___________________________________ ___________________________________ Ksp = [Ag+][I-] = 8.3 x 10-17
b. 1.7 x 10-16
Ksp = x(x) = x2
c. 2.7 x 10-6
___________________________________ x = solubility = [Ag+] = [I-]
= (8.3 x 10-17)0.5 = 9.1 x 10-9
d. 9.1 x 10-9
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Common Ion Effect
50 ___________________________________ Common ion effect: a shift in the equilibrium,
based on Le Châtelier’s principle, when additional
___________________________________ ion already present in a solution is added.
Example
___________________________________ Sodium hydroxide is added to a saturated solution of
___________________________________ magnesium hydroxide until the [OH-] is 0.010 M.
Mg(OH)2 (s)
Mg2+ (aq) + 2 OH- (aq)
___________________________________ The addition of hydroxide ions shifts the equilibrium
to the left, reducing the magnesium ions in solution.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 51 ___________________________________ ___________________________________ Common Ion Effect Practice
___________________________________ What is the [Mg2+] in solution when sodium hydroxide
is added to a saturated Mg(OH)2 solution until the
___________________________________ [OH-] = 0.010 M? (Ksp = 5.6 x 10-12)
Equation
Mg(OH)2 (s)
Initial (M)
Change (M)
Equil. (M)
___________________________________ Mg2+ (aq) + 2 OH- (aq)
0
+x
x
Ksp = x(0.010) = 5.6 x
___________________________________ 0
0.010
0.010
___________________________________ 10-12
___________________________________ x = 5.6 x 10-12/0.010 = 5.5 x 10-8 M
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 52 ___________________________________ Buffer Solution
___________________________________ Buffer solution: resists changes in pH when diluted or
___________________________________ small amounts of acid or base are added.
Buffers are prepared by mixing together
___________________________________ (usually equimolar amounts) of:
___________________________________ 1. A weak acid with a salt containing its conjugate base.
2. A weak base with a salt containing its conjugate acid.
___________________________________ Buffer capacity: extent to which a buffer can absorb
added acid or base and still maintain the pH.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 53 ___________________________________ ___________________________________ Buffers
___________________________________ Consider a buffer prepared using 0.1 M CH3COOH
and 0.1 M NaOOCCH3.
___________________________________ The solution contains an acid (CH3COOH) which
___________________________________ can neutralize base when added,
so the pH does not change.
CH3COOH (aq) + OH- (aq)
___________________________________ CH3COO- (aq) + H2O (l)
The solution also contains a base (CH3COO-) which can
___________________________________ neutralize acid when added, so the pH does not change.
CH3COO- (aq) + H3O+ (aq)
CH3COOH (aq) + H2O (l)
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 54 ___________________________________ ___________________________________ Buffers
___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 55 ___________________________________ Learning Objectives
___________________________________ 16.1 Rates of Reaction
List the factors that affect the rate of a chemical reaction.
___________________________________ 16.2 Chemical Equilibrium
___________________________________ Define a reversible chemical reaction and explain what
is occurring in a chemical reaction at equilibrium.
___________________________________ 16.3 Le Châtelier’s Principle
___________________________________ Use Le Châtelier’s principle to predict the changes
that occur when concentration, temperature or
volume is changed in a system at equilibrium.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 56 ___________________________________ ___________________________________ Learning Objectives
16.4 Equilibrium Constants
___________________________________ Write the general expression for the
equilibrium constant for a reaction.
___________________________________ 16.5 Ion Product Constant for Water
___________________________________ Calculate the concentrations of H+ and OH- in a
solution using the ion product constant for water.
___________________________________ 16.6 Ionization Constants
___________________________________ Use the ionization constant of a reactant in an equilibrium
expression to find the percent ionization of a substance
in solution and to find the pH of a weak acid.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 57 ___________________________________ ___________________________________ Learning Objectives
___________________________________ 16.7 Solubility Product Constant
___________________________________ Use the solubility product constant to calculate the
solubility of a slightly soluble salt and to determine
whether a precipitate will form in a solution.
___________________________________ ___________________________________ ___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.