Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
Equilibrium
Reminder: Gases must be studied in closed containers!
-Some reactions are reversible (proceed in two directions):
Reactants form Products
AND
Products reform Reactants
The forward reaction is the one in which reactants form products.
The reverse reaction is the one in which products form reactants.
Reactants are ALWAYS to the left of the arrow in a chemical equation.
Products are ALWAYS to the right of the arrow in a chemical equation.
REACTANTS ↔ PRODUCTS
→= fwd reaction
←= reverse reaction
There will never only be one arrow pointing to the left (←).
EQUILIBRIUM (dynamic equilibrium)
-When the RATE of the forward reaction is EQUAL to the RATE of the reverse reaction
RATE = RATE
-when a system is at equilibrium the concentrations of the reactant and product substances are
NOT necessarily equal. The CONCENTRATIONS are CONSTANT.
RATES EQUAL
CONCENTRATIONS CONSTANT
Types of Equilibria
↙
↘
Physical
Chemical
↙
↘
phase
solution
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
Phase Equilibrium
1) The RATE at which (s) turns to (l) = the RATE at which (l) turns to (s)
rate of freezing = rate of melting
(s) ↔ (l)
For H2O, at 1 atm, this will occur at 0 ℃
2) The RATE at which (l) turns to (g) = the RATE at which (g) turns to (l)
rate of boiling = rate of condensation
(l)↔(g)
For H2O at 1 atm this will occur at 100 C
or in a closed container under any conditions of T&P
3) The RATE at which (s) turns to (g) = the RATE at which (g) turns to (s)
rate of sublimation = rate of deposition
(s)↔(g)
REMINDER: CLOSED CONTAINER FOR GASES
Solution Equilibrium
Remember that temperature affects solubility. So, temperature is constant at equilibrium.
Review question: What type of solution is at equilibrium? SATURATED
rate of dissolving = rate of crystallization
(the rate at which a solute dissolves is equal to the rate at which the dissolved solute crystallizes)
ex) NaCl (s)↔ NaCl (aq)
ex) CO2 (g) ↔ CO2 (aq)
Table F should already be memorized. Remember the note at the bottom of table F: insoluble indicates
low solubility. Table F is qualitative. We are now ready for the quantitative description of solubility. All
salts have their own degree of solubility (how soluble is the salt?).
CONCENTRATIONS ARE CONSTANT at equilibrium. So, the concentration of the dissolved ions will not
change, and the concentration of solid (not dissolved) solute will not change.
Solubility Product Constant
-The solubility product constant (Ksp) is an equilibrium expression that relates (expresses) the molar
concentrations of the dissolved ions.
-Ksp shows the degree of solubility-how soluble the salt is.
-Solids (and liquids) are NEVER included in an equilibrium expression of concentration because their
concentrations are not capable of being changed (equilibrium or not)!
-Only gases and aqueous solutions will be included in equilibrium expressions.
-will change with a change in temperature
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒
-[ ] = molar concentration = Molarity = 𝑙𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
[𝑝𝑟𝑜𝑑𝑢𝑐𝑡]
Ksp = [𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡]
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
Examples (Show the Ksp equilibrium expression for each):
1. NaCl
NaCl(s)↔ Na+(aq) + Cl-(aq)
Ksp = [Na+][Cl-]
2. CaC2O4
CaC2O4(s) ↔ Ca2+(aq) + C2O42-(aq)
Ksp =
3. CaF2
CaF2(s) ↔ Ca2+(aq) + 2F-(aq)
Ksp = [Ca2+][F-]2
NOTE: when there will be more than one mole of a species, the coefficients becomes the exponents in
the equilibrium expression (in this case the Ksp).
4. MgF2
5. Na2CO3(s)
What does a large Ksp mean? Lots of ions, very soluble
What does a small Ksp mean? Few ions, not very soluble
Time to add the math:
1. Calculate the Ksp of silver bromide if the molar solubility of both silver ions and bromide ions are
7.0 X 10-7. Show all work.
2. SrF2 has a strontium ion concentration of 8.7 X 10-4 M and a fluoride ion concentration of 1.74 X 10-3
M. Calculate the Ksp. Show all work.
3. Calculate the molar solubility of lead (II) sulfate if the Ksp is 1.6 X 10-8. Show all work.
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
4. Calcium fluoride has a Ksp = 3.2 X10 -11
Calculate the calcium ion and fluoride ion concentration at equilibrium. Show all work.
Chemical Equilibrium
RATE of the fwd rx = RATE of the reverse rx
-think treadmill
-think stair climber
-think of a 100 piece puzzle in which you have connected 80 pieces. You have 20 pieces to fit in.
Every time you put a piece into the puzzle, your friend takes a different piece out. So, pieces are
constantly being moved, but the puzzle always remains 80% complete.
Equilibrium can be disturbed.
A stress/stressor is anything that alters (ruins, disturbs, breaks) equilibrium.
Example: If you run out of energy on the treadmill, but the treadmill keeps moving, you fall off!!
Example: If your friend starts taking two pieces out for every one piece you put into a puzzle, the
equilibrium will shift and the puzzle will no longer stay 80% completed.
After being disturbed, a system will find a "new" equilibrium.
Le Chatelier's Principle
-when a stress is applied to a system (rx) at equilibrium, the rx/system/equilibrium will shift to relieve
the stress.
There are only 2 ways a reaction can shift:
shift right: means the forward reaction will be faster than the reverse reaction until a new
equilibrium is reached
shift left: means the reverse reaction will be faster than the forward reaction until a new
equilibrium is reached.
possible stress:
1. Concentration
2. Temperature
3. Pressure (gases only)
Catalysts:
-Introduction/use of a catalyst is NOT a stress. -A catalyst speeds up both the forward and the reverse
reactions equally.
-Catalysts do NOT cause a shift.
-Catalysts do NOT alter equilibrium.
Honors Chemistry
Kinetics and Equilibrium
Concentration as a stress
example:
A + B + energy  C + D
1) If [A] increases:
the reaction will shift to the:
[B] will:
[C] will:
[D] will:
5) If [A] decreases:
the reaction will shift to the:
[B] will:
[C] will:
[D] will:
2) If [B] increases:
the reaction will shift to the:
[A] will:
[C] will:
[D] will:
6) If [B] decreases:
the reaction will shift to the:
[A] will:
[C] will:
[D] will:
3) If [C] increases:
the reaction will shift to the:
[A] will:
[B] will:
[D] will:
7) If [C] decreases:
the reaction will shift to the:
[A] will:
[B] will:
[D] will:
4) If [D] increases:
the reaction will shift to the:
[A] will:
[B] will:
[C] will:
8) If [D] decreases:
the reaction will shift to the:
[A] will:
[B] will:
[C] will:
example:
A + B  C + D + energy
Then↓
If: 
[A] incr
[B] incr
[C] incr
shift
[A]
xxxxxxx
[B]
xxxxxxx
[C]
xxxxxxx
[D]
-If
-If
-If
-If
HW: chapter 13 all odd questions
[D] incr
[A] decr
[B] decr
[C] decr
[D] decr
xxxxxxx
xxxxxxx
xxxxxxx
xxxxxxx
something on the L incr, then the shift will be to the R.
something on the R incr, then the shift will be to the L.
something on the L decr, then the shift will be to the L.
something on the R decr, then the shift will be to the R.
-When shift R: everything on the R incr and everything on the L decr.
-When shift L: everything on the L incr and everything on the R decr.
xxxxxxx
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
Common Ion Effect: using a substance other than one of the reactants or products to change the
concentration of an ion in the reaction.
This is usually a "common ion" which means the new substance has the same ion as one of the
reactant or product substances.
ex: NaCl(s) ↔Na+(aq) + Cl-(aq)
In terms of Le Chatelier's principle, explain what will happen when KCl is introduced to the system.
(this is how you increase the concentration of one of the reactants or products)
It also could be a different ion that reacts with one of the reactant or product ions.
ex: NaCl(s) ↔Na+(aq) + Cl-(aq)
In terms of Le Chatelier's principle, explain what will happen when AgNO3 is introduced to the system.
(this is how you decrease the concentration of one of the reactants or products)
Example:
N2(g) + 3H2(g) ↔2NH3(g) + 91.8 kJ
1. Which way will the reaction shift if [N2] increases?
2. What will happen to the [NH3] if [H2] decreases?
3. What will happen to the [N2] if [NH3] increases?
Temperature as a stress
Reminder: Temp is a measure of a.k.e.
Increasing temp:
-increasing the temperature speeds up all (endo and exo) reactions.
-BUT: increasing temperature favors endothermic reactions (speeds up an endo rx more than the exo rx
in a reversible reaction)
-When temperature increases, it is as if "energy" is another substance in the chemical equation. So, the
shift will be away from the "energy" side.
Decreasing temp:
-decreasing the temperature slows all (endo and exo) reactions.
-BUT: decreasing temperature favors exothermic reactions (slows down an endo rx more than the exo rx
in a reversible reaction)
-When temperature decreases, it is as if "energy" is another substance in the chemical equation. So, the
shift will be towards the "energy" side.
A + B + energy ↔ C + D
If temperature is increased:
the equilibrium will shift to the:
[A] will:
[B] will:
[C] will:
[D] will:
If temperature is decreased:
the equilibrium will shift to the:
[A] will:
[B] will:
[C] will:
[D] will:
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
A + B ↔ C + D + energy
If temperature is increased:
the equilibrium will shift to the:
[A] will:
[B] will:
[C] will:
[D] will:
If temperature is decreased:
the equilibrium will shift to the:
[A] will:
[B] will:
[C] will:
[D] will:
Example:
N2(g) + 3H2(g) ↔ 2NH3(g) + 91.8 kJ
What would be the effect on equilibrium if temperature is increased?
What would be the effect on equilibrium if temperature is decreased?
What would happen to the concentration of nitrogen if temperature is increased?
What would happen to the concentration of ammonia if temperature is decreased?
Pressure as a stress: (gases only)
Reminders:
-(g) represents a gas
-coefficients represent the number of moles of a substance
-If pressure increases, the equilibrium will shift from the side with more gas particles to the side with
fewer (less) gas particles.
-If pressure decreases, the equilibrium will shift from the side with fewer (less) gas particles toward the
side with more gas particles.
*Substances in the equations that are not in gas phase have no effect in determining the number of
gas particles!
example:
N2(g) + 3H2(g)
 2NH3(g) + 91.8 kJ
If pressure is increased:
the equilibrium will shift to the:
[N2] will:
[H2] will:
[NH3] will:
If pressure is decreased:
the equilibrium will shift to the:
[N2] will:
[H2] will:
[NH3] will:
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
What effect does the introduction of a catalyst have on equilibrium?
-no effect
-a catalyst speeds up both the forward and the reverse reactions equally.
-REMINDER: a catalyst speeds up a reaction by lowering the activation energy/providing an
alternate route.
Not all reactions are reversible. Reactions that are not reversible are said to "go to completion." This
means that only the forward reaction occurs. This happens when a precipitate is formed or a gas forms
(and is not collected).
List all the ways to increase the production of ammonia according to the Haber Process at equilibrium
(Heat of the reaction is -91.8kJ)
Equilibrium constants for chemical equilibrium Keq = Kc
Keq =
[𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠]
[𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠]
[ ] = Concentration = Molarity = Moles of solute/Liters of solution
-All equilibrium constants/equilibrium expressions include ONLY gases and aqueous, NEVER solids or
liquids.
-Keq tells us which reaction, the forward or reverse is favored
-All Equilibrium Constants are CONSTANTS and never change!!
-The only thing that can ever change an Equilibrium Constant is Temperature!
-Large K(eq) - means that there is more product; therefore the forward reaction/products are favored
-Small K(eq) - means that there is more reactant; therefore the reverse reaction/reactants are favored
2A(g) + 3B(g)  4C(g) + 5D(g)
Equilibrium expression = [C]4[D]5
[A]2[B]3
N2(g) + 3H2(g) ↔ 2NH3(g)
Write the equilibrium expression:
Kc are experimentally determined and are tabulated or can be solved for using some more math!!
Calculating the Keq:
1. What is the Keq for the following equilibrium at 500 0C
N2(g) + 3H2(g) ↔ 2NH3(g)
[N2] = 0.44 M
[H2] = 0.44 M
[NH3] = 2.2 M
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
2. What is the value of Keq for the following equilibrium:
CO2(g) + H2(g) ↔ CO(g) + H2O(g)
Given:
[CO(g)] = 0.20 M
[H2O(g)] = 0.30 M
[CO2(g)] = 0.30 M
[H2(g)] = 0.033 M
3.
CO2(g) + H2(g) ↔ CO(g) + H2O(g)
For the reaction of carbon dioxide and hydrogen, the equilibrium concentration are CO2 = 0.25 M, H2 =
0.80 M, H2O = 0.50 M. What is the equilibrium concentration for CO if the Keq = 0.11
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
Using the Equilibrium Constant (ICE CHARTS)
1. A Closed system initially contains 0.01 M H2 and 0.02 M I2 at a temperature of 4480C is allowed to
reach equilibrium. Analysis of the equilibrium mixture shows that the concentration of the HI is 0.0187
M. Calculate the Kc for this reaction at 4480C.
H2(g) + I2(g) ↔ 2HI(g)
2. The initial concentration of SO3 is 0.50M in a sealed container. If the equilibrium concentration of the
SO3 is 0.20M, calculate the Kc for the reaction
2SO3(g) ↔ 2SO2(g) + O2(g)
3. A 500.0 mL flask is filled with 1 mol of H2 and 2 mol of I2. The value of Kc = 4.9 X 10 -12. What are the
equilibrium concentrations of H2, I2 and HI?
H2(g) + I2(g) ↔ 2HI(g)
Honors Chemistry
Kinetics and Equilibrium
HW: chapter 13 all odd questions
4. A 500.0 mL flask is filled with 2 mol of H2 and 2 mol of I2. The value of Kc = 4.9 X 10 -12. What are the
equilibrium concentrations of H2, I2 and HI?
H2(g) + I2(g) ↔ 2HI(g)
5. If a 500.0 ml vessel containing 0.60 mol of HI is sealed and allowed to reach equilibrium calculate the
equilibrium concentrations of HI, H2 and I2 if the Kc = 9
2HI(g) ↔ H2(g) + I2(g)