1. Get out a piece of paper to take notes on.
Turn in your Take Home Exams
If you didn’t write this down yesterday, write it down now:
Equilibrium SRR: Pgs # , , …Write your own guided outline.
Get out a piece of paper to take notes on.

2. Test and “F” Information
Overall Average: 52.74%...Failing
2nd: 54.53%
4th: 51.26%
5th: 58.95%
6th: 46.24%
High: 112%
Low: 3%
“F”’s
Was 12 and 13%
Now 30 and 32.6%

3. I SEE LOTS OF RETAKE’S IN YOUR FUTURES!!!
Must be done by March 17th
Test corrections required

4. What is Equilibrium?

5. This is not Equilibrium?

6. Chemical Equilibrium in Nature: (The formation of stalagmites and Stalactites)

7. Equilibrium=

8. Chemical Equilibrium Consider the following reactions:
H2(g) + O2(g)  H2O(g)…(1)
and
H2O(g)  H2(g) + O2(g) …(2)
Reaction (2) is the reverse of reaction (1).
At equilibrium the two opposing reactions occur at the same rate.
Concentrations of chemical species do not change once equilibrium is established.

9. Expression for Equilibrium Constant
Consider the following equilibrium system:
wA + xB ⇄ yC + zD
Kc =
The numerical value of Kc is calculated using the concentrations of reactants and products that exist at equilibrium.
Include only substances in the gas or aqueous phase. Solid’s and water’s concentrations do not change during a chemical reaction.

10. Expressions for Equilibrium Constants
Examples:
N2(g) + 3H2(g) ⇄ 2NH3(g); Kc =
PCl5(g) ⇄ PCl3(g) + Cl2(g); Kc =

11. Interpretation of the Equilibrium Constant
For K>1, we can state that the amount of product is greater than the amount of reactant. The equilibrium is shifts to the right.
Likewise, for K<1, the amount of reactants is much greater than the products. The equilibrium shifts to the left.

12. Calculate K for the following reaction given the following equilibrium concentrations of PCl5, PCl3, and Cl2.
PCl5(g) ⇄ PCl3(g) + Cl2(g) K = ??
(M):

13. What is the equilibrium concentration of Br2 if [HBr] = 0
What is the equilibrium concentration of Br2 if [HBr] = 0.35 M and [H2] = 0.22 M at equilibrium?
H2(g) + Br2(g) ⇄ 2HBr(g) K = 62.5

14. Equilibrium constant is used to predict the direction of net reaction
For a reaction of known Kc value, the direction of net reaction can be predicted by calculating the reaction quotient, Qc.
Qc is called the reaction quotient, where for a reaction such as:
aA + bB ⇄ cC + dD;
Qc has the same expression as Kc , but
Qc is calculated using concentrations that are not necessarily at equilibrium.

15. What does the reaction quotient tell us?
If Qc = Kc,  the reaction is at equilibrium;
If Qc < Kc,  the reaction is not at equilibrium and there’s a net forward reaction;
If Qc > Kc,  the reaction is not at equilibrium and there’s a net reverse reaction.

16. Chemical Kinetics Chemical kinetics: the study of reaction rate
Factors affecting reaction rate: Concentrations of reactants Catalyst Temperature Surface area of solid reactants or catalyst

17. Factors that Affect Reaction Rate
Temperature
Kinetic Theory: Increasing temperature means the molecules move faster.
Concentrations of reactants
More reactants mean more collisions if enough energy is present
Catalysts
Speed up reactions by lowering activation energy
Surface area of a solid reactant
Bread and Butter theory: more area for reactants to be in contact

18. D[A] = change in concentration of A over time period Dt
Reaction rate is the change in the concentration of a reactant or a product with time (M/s).
A B
rate = -
D[A] Dt
D[A] = change in concentration of A over
time period Dt
rate =
D[B] Dt
D[B] = change in concentration of B over
time period Dt
Because [A] decreases with time, D[A] is negative.

19. Calculating reaction rate
The concentrations of N2O5 are M and M at 600 and 1200 s after the reactants are mixed at the appropriate temperature. Evaluate the reaction rates for
2 N2O5 = 4 NO2 + O2
Solution: ( – ) e-2 M Decomposition rate of N2O5 = – ———————— = – —————— – s
= 5.2e-6 M s-1.
Note however, rate of formation of NO2 = 1.02e-5 M s-1. rate of formation of O2 = 2.6e-6 M s-1.

20. Reaction Rates and Stoichiometry
To generalize, for the reaction
aA + bB
cC + dD
Reactants (decrease)
Products (increase)

21. Le Châtelier’s Principle
The Le Châtelier's principle states that:
when factors that influence an equilibrium are altered, the equilibrium will shift to a new position that tends to minimize those changes.
Factors that influence equilibrium:
Concentration, temperature, and addition of a catalyst

22. The Effect of Changes in Concentration
Consider the reaction: N2(g) + 3H2(g) ⇄ 2 NH3(g);
If [N2] and/or [H2] is increased, Qc < Kc
 a net forward reaction will occur to reach new equilibrium position.
If [NH3] is increased, Qc > Kc, and a net reverse reaction will occur to come to new equilibrium position.

23. Concentration Changes
Add more reactant  Shift to products
Remove reactants  Shift to reactants
Add more product  Shift to reactants
Remove products  Shift to products

24. Temperature Changes Exothermic Reactions
Consider heat as a product in exothermic reactions.
Add heat 
Shift to reactants
Remove heat 
Shift to products
A + B = AB + Heat

25. Temperature Changes Endothermic Reactions
Consider heat as a reactant in endothermic reactions.
Add heat 
Shift to products
Remove heat 
Shift to reactants
A + B + heat = AB

26. Catalysts
Adding a catalyst increases the rate at which equilibrium is achieved, but it does not change the composition of the equilibrium mixture.

28. S8(g) + 12O2(g)  8 SO3(g) + 808 kcals
Given:
S8(g) O2(g)  8 SO3(g) kcals
What will happen when ……
Oxygen gas is added?
The reaction vessel is cooled?
Sulfur trioxide is removed?
A catalyst is added to make it faster?
Shifts to prodcuts 
Shifts to Products – to replace heat
Shift to products to replace it!
No change!