Dr. Lara Baxley
Chem 201B
Chapter 14 Notes
page 1
Chem 201B
Chapter 14 Notes: Equilibrium
I. Equilibrium and Equilibrium Constant
A. Equilibrium Expression You learned about this in JITL#1:
1. What is the big difference between how you determine equilibrium expressions
and how you determine rate laws?
2. Write the equilibrium expressions for each of the following equations (equations
are not balanced).
a. CH4(g) + F2(g) ⇌ CF4(g) + HF(g)
b.
S8(s) + F2 (g) ⇌ SF6(g)
c.
H2O(l) + H3PO4(aq) ⇌ H3O+(aq) + PO43– (aq)
3. At a certain temperature, the reaction CO(g) + 2 H2(g) ⇌ CH3OH(g) has K = 0.500. If
a reaction mixture at equilibrium contains 0.180 M CO and 0.220 M H2, what is the
concentration of CH3OH?
B. Reaching Equilibrium
Dr. Lara Baxley
Chem 201B
C. Reaching Equilibrium: Penny Example
Chapter 14 Notes
page 2
Q = [products]
[reactants]
Dr. Lara Baxley
Chem 201B
D. Significance of the Magnitude of K
• Which of these reactions has the highest K?
• Which has the lowest K?
II. Gaseous Reactions
Chapter 14 Notes
page 3
Dr. Lara Baxley
Chem 201B
1. For the reaction, CO(g) + 2 H2(g) ⇌ CH3OH(g)
KC = 3.8 x 10−2 at 200 °C. What is KP?
What if ∆ng = 0?
eg: 2 HI(g)  H2(g) + I2(g)
III. Reaction Direction: Comparing Q and K
A. Reaction quotient, Q
2. For the reaction, COCl2 ⇌ CO + Cl2, Kc = 8.3 X 10–4 (at 360 °C)
If at a given time in the reaction, [COCl2] = 0.18 M, [CO] = 0.35 M,
[Cl2] = 0.12 M which direction will the reaction proceed?
Chapter 14 Notes
page 4
Dr. Lara Baxley
Chem 201B
Chapter 14 Notes
page 5
IV. Equilibrium Calculation
A) Calculating Kc from initial and change
3. In a 2.00 L vessel, 3.8 mol CO are combined with 12.0 mol H2. At equilibrium, there
are 0.60 mol CO. What are the concentrations of the other substances and what is
the equilibrium constant?
CO(g) + 3 H2(g) ⇌ CH4(g) + H2O(g)
B) Calculating conc. using Kc and initial concs
4. If 0.100 mol of CO2 and 0.100 mole of H2(g) are placed in a 1.00 L reaction vessel at
500 °C, What are the equilibrium concentrations. At this temp, Kc = 0.246
CO2(g) + H2(g)
⇌ CO(g) + H2O(g)
Dr. Lara Baxley
Chem 201B
Chapter 14 Notes
page 6
C. Starting with reactants and products:
5. What are the equilibrium concentrations for the same reaction as the previous
question at the same temperature, but starting with 0.100 mol each of CO2 and H2
and 0.0600 mol each of CO and H2O in 1.00 L vessel?
CO2(g) + H2(g) ⇌
CO(g) +
H2O(g)
D. Using the quadratic equation
6. H2 and I2 are pumped into a vessel at 458 °C such that the partial pressure of H2 is
1.00 atm and the partial pressure of I2 is 2.00 atm. What will be the partial
pressures of H2, I2 and HI at equilibrium?
H2(g) + I2(g) ⇌ 2 HI(g)
Kp = 49.7
Dr. Lara Baxley
Chem 201B
Chapter 14 Notes
page 7
E. Estimating x
7. If 0.45 mol H2S is put in a 3.0 L container, what is the equilibrium concentration of
H2 at 700 °C where Kc = 9.30 X 10–8?
Dr. Lara Baxley
Chem 201B
V. Le Châtelier’s Principle
A. Shifting Reactions
8. 2 NOCl(g) ⇌ 2 NO(g) + Cl2(g), ∆H = + 77.1 kJ
How will the reaction shift, and how will the value of K change if…
a. NOCl is removed
b. A compound is added that reacts with Cl2
c. The temperature increases
d. The volume of the container decreases
e. Pressure change due to adding an inert gas, such as He
B. Calculating K at different temps
van’t Hoff Equation
Chapter 14 Notes
page 8
Dr. Lara Baxley
Chem 201B
Chapter 14 Notes
page 9
VI. Manipulating equations
A. Changing Direction
9. 2 SO3 ⇌ 2 SO2 + O2 Kc = 7.0 x 1025. What is the Kc of 2 SO2 + O2 ⇌ 2 SO3
B. Multiplying Coefficients by a Factor
10. Using previous equation. What is Kc of 6 SO3 ⇌ 6 SO2 + 3 O2
C. Adding Chemical Equilibria
11. N2(g) + O2(g) ⇌ 2 NO(g)
2 NO(g) + O2(g) ⇌ 2 NO2(g)
N2(g) + 2 O2(g) ⇌ 2 NO2(g)
K1 = 4.3 x 10−25
K2 = 6.4 x 109
Ksum = ?