Ch 6: Chemical Equilibrium
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What is Equilibrium?
Equilibrium Constant, K
Equilibrium Expressions Involving Pressures
Activity - read text
Heterogeneous Equilibria
Applications of Equilibrium Constant
Solving Equilibrium Problems
Le Chatelier’s Principle - very important
Equilibria Involving Real Gases - read text
Week 9
CHEM 1310 - Sections L and M
1
Le Châtelier’s Principle
A system in equilibrium that is subjected to stress
reacts in a way to counteract the stress.
 Adding or Removing
Reactants or Products
 Change in Volume or
Pressure of a System
 Change in Temperature
Week 9
(1850-1936)
CHEM 1310 - Sections L and M
2
Le Châtelier’s Principle
 What happens when reactants or products are
added to a system?
Cu(H2O)42+ (aq) + 4 Cl- (aq) ↔ CuCl22- (aq) + 4 H2O (l)
At equilibrium: blue-green color
After addition of HCl: solid green
After addition of H2 O:
Week 9
CHEM 1310 - Sections L and M
3
1
Le Châtelier’s Principle
 What happens when a reactants is removed from
a system?
Cu(H2O)42+ (aq) + 4 Cl- (aq) ↔ CuCl22- (aq) + 4 H2O (l)
Ag+
Ag+(aq) + Cl- (aq) ↔ AgCl(s)
Result:
Week 9
See enhancement of blue color
Shift from right to left
CHEM 1310 - Sections L and M
4
Le Châtelier’s Principle
 What happens when the volume of the
system is reduced?
PCl5(g) ↔ PCl3(g) + Cl2(g)
PV = nRT
As V↓ P↑
1 mole of
reactants
2 moles of
products
Counteract pressure increase by shifting reaction to
side where there are fewer molecules
Week 9
CHEM 1310 - Sections L and M
5
Le Châtelier’s Principle
 What happens when the temperature of the
system changes?
H2O (s) ↔ H2O (l)
Adding energy (as heat) shifts equilibrium to right
Melting: endothermic (absorbs heat)
Removing energy (i.e. putting ice in freezer) shifts
equilibrium to left
Freezing: exothermic (liberates heat)
Week 9
CHEM 1310 - Sections L and M
6
2
PRS Questions
 The equilibrium constant for A + 2B  3C is
2.1 x 10-6. Determine the equilibrium
constant for 2A + 4B  6C.
1. 4.2 x 10-6
2. 4.4 x 10-12
3. 2.3 x 1011
4. 1.8 x 10-11
5. None of these
Week 9
CHEM 1310 - Sections L and M
7
PRS Questions
 The equilibrium constant for A + 2B  3C is
2.1 x 10-6. Determine the equilibrium
constant for 2A + 4B  6C.
1. 4.2 x 10-6
2. 4.4 x 10-12
3. 2.3 x 1011
4. 1.8 x 10-11
5. None of these
Week 9
CHEM 1310 - Sections L and M
8
PRS Question
 Consider the following reaction
2 HF(g)  H2(g) + F2(g) K = 1.00 x 10-2)
Given 1.00 mole HF, 0.500 mol H2 and 0.75 mol F2 are
mixed in a 5.00-L flask, determine the reaction quotient, Q,
and the net direction to achieve equilibrium.
1.
2.
3.
4.
5.
Week 9
Q = 0.150; equilibrium shifts to the right
Q = 0.375; equilibrium shifts to the left
Q = 0.150; equilibrium shifts to the left
Q = 0.375; equilibrium shifts to the right
Q = 0.150; the system is at equilibrium
CHEM 1310 - Sections L and M
9
3
PRS Question
 Consider the following reaction
2 HF(g)  H2(g) + F2(g) K = 1.00 x 10-2)
Given 1.00 mole HF, 0.500 mol H2 and 0.75 mol F2 are
mixed in a 5.00-L flask, determine the reaction quotient, Q,
and the net direction to achieve equilibrium.
1.
2.
3.
4.
5.
Q = 0.150; equilibrium shifts to the right
Q = 0.375; equilibrium shifts to the left
Q = 0.150; equilibrium shifts to the left
Q = 0.375; equilibrium shifts to the right
Q = 0.150; the system is at equilibrium
Week 9
CHEM 1310 - Sections L and M
10
PRS Question
 To increase the value of K for the following
exothermic reaction, you must…
2 Hs(g) + O2(g)  H2O(g)
1. Increase the total pressure
2. Decrease the total pressure
3. Increase the temperature
4. Decrease the temperature
5. Two of these
Week 9
CHEM 1310 - Sections L and M
11
4