1. Definition Class Demo with hall
Chemical Equilibrium – when the rate of the forward and reverse reactions are equal
Dynamic – Reactions at eq never stop
Equilibrium DOES NOT mean that the amount of reactants and products are equal. They have reached an unchanging ratio

2. Definition
Equilibrium GI

3. Cis Trans

6. Definition NaCl (s)  Na+(aq) + Cl-(aq) [unsaturated]
NaCl (s)  Na+(aq) + Cl-(aq) [saturated]

7. Graphs 2. Starting with all products (NO2) N2O4(g)  2NO2(g)
Clear Brown
Cold Hot
Starting with all reactants (N2O4)
2. Starting with all products (NO2)
Graphs

9. Eq. Constants Kc = Eq. Constant involving molarity a. Molarity = [ ]
b. Example = [0.50 M]
2. Kp = Eq. Constant involving pressure
a. Atmospheres
b. We live at about 1 atm
Generic Example
aA + bB  cC + dD

10. Eq. Constants
2O3(g)  3O2(g) 2NO(g) + Cl2(g)  2NOCl(g) H2(g) + I2(g)  2HI(g)

11. Heterogeneous Equilibrium
More than one state is present
Exclude solids and liquids from K. (not considered to have a molarity or pressure)

12. Heterogeneous Eq.
SnO2(s) + 2CO(g)  Sn(s) + 2CO2(g) Pb(NO3)2(aq)+Na2SO4(aq)PbSO4(s) +2NaNO3(aq) Ba2+(aq) + SO42-(aq)  BaSO4(s)

13. A Note About Water Exclude liquid water (often the solvent)
Keep gaseous water
Examples
CO2(g) + H2(g)  CO(g) + H2O(l)
3Fe(s) + 4H2O(g)  Fe3O4(s) + 4H2(g)

14. An example
CO(g) + Cl2(g)  COCl2(g)
Kc = 4.6 X 109
Rules
K>>1 Favors the products
K<<1 Favors the reactants
K~1 Reactants ~ Products

15. Does the following reaction favor the products or reactants?
N2(g) + O2(g)  2NO(g)
Kc = 1 X 10-30
For the following reaction, Kc = 794 at 298 K and Kc = 54 at 700 K. Should you heat or cool the mixture to promote the formation of HI?
H2(g) + I2(g)  2HI(g)

16. Kc= 2.5 X 10-30 for N2(g) + O2(g)  2NO(g) calculate Kc for:
2NO(g)  N2(g) + O2(g)
Calculate Kc for
½ N2(g) + ½ O2(g)  NO(g)
3. The Kc for N2(g) + 3H2(g)  2NH3(g) is 4.43 X Calculate Kc for:
2N2(g) + 6H2(g)  4NH3(g)

17. Converting Between Kc and Kp Kp = Kc (RT)Dn R = 0
Converting Between Kc and Kp Kp = Kc (RT)Dn R = L atm/mol K T = Kelvin Temperature Dn = change in number of moles of gas

18. Calculate Kp for the following reaction at 300 oC: N2(g) + 3H2(g)  2NH3(g) Kc = 9.60 ANS: (4.34 X 10-3)

19. Calculate Kp for the following reaction at 1000 K: 2 SO3(g)  2SO2(g) + O2(g) Kc = 4.08 X 10-3 ANS: 0.335

20. A mixture is allowed to reach eq. At eq. , the vessel contained 0
A mixture is allowed to reach eq.. At eq., the vessel contained M H2, M N2, and M NH3. Calculate the equilibrium constant.
N2(g) + 3H2(g)  2NH3(g)
(Ans: )

21. 2. At eq. , a vessel contained 0. 00106 M NO2Cl, 0. 0108 M NO2, and 0
2. At eq., a vessel contained M NO2Cl, M NO2, and M Cl2. Calculate the equilibrium constant.
NO2Cl(g)  NO2(g) + Cl2(g)
(Ans: )

22. 3. A mixture of mol of H2 and mol of I2 is placed in a 5.00 L flask and allowed to reach eq.. At eq., the mixture is found to be [HI] = M. Calculate Kc.
H2(g) + I2(g)  HI(g)
(Ans: 51)

23. 4. A vessel is charged with 0. 00609 M SO3. At eq
4. A vessel is charged with M SO3. At eq., the SO3 concentration had dropped to M SO3. What is the value of Kc?
SO3(g)  SO2(g) + O2(g)
(Ans: )

24. mol of HI was placed in a 5.00 L flask and allowed to decompose. At eq. It was found that the vessel contained mol of I2. What is the value of Kc?
HI(g)  H2(g) + I2(g)
(Ans: )

25. An eq. mixture of gases is analyzed
An eq. mixture of gases is analyzed. The partial pressure of nitrogen is atm and the partial pressure of hydrogen is atm. If Kp is 1.45 X 10-5, what is the partial pressure of ammonia?
N2(g) + 3H2(g)  2NH3(g)

26. PCl5(g)  PCl3(g) + Cl2(g)
Consider the following equilibrium:
PCl5(g)  PCl3(g) + Cl2(g)
At equilibrium, the partial pressure of PCl5 and PCl3 are measured to be atm and atm, respectively. If Kp = 0.497, what is the partial pressure of Cl2? (1.22 atm)
Suppose at equilibrium the partial pressure of PCl5 is 2.00 atm. Calculate the partial pressure of PCl3 and Cl2 . Assume Kp is still and only PCl5 was initially in the flask. (0.997 atm)

27. 0 = ax2 + bx + c
x = -b + \/ b2 – 4ac 2a
2x2 + 4x = 1

28. 1. A gas cylinder is charged with 1
1. A gas cylinder is charged with 1.66 atm of PCl5 and allowed to reach eq.. If the Kp= 0.497, what are the pressures of all the gases at equilibrium? PCl5(g)  PCl3(g) + Cl2(g) (Ans: 0.97 atm, atm)

29. 2. A 1. 000 L flask is filled with 1. 000 mol of H2 and 2
2. A L flask is filled with mol of H2 and mol of I2. The Kc = What are the concentrations of all the gases at equilibrium?
H2(g) + I2(g)  2HI(g)
(Ans: M, M, 1.87 M)

30. Do I always need the quadratic, or can I cheat
Do I always need the quadratic, or can I cheat? The equilibrium constant for the following reaction is NO(g)  N2(g) + O2(g) If the initial concentration of NO is M, calculate the equilibrium concentrations of NO, N2 and O2. (Ans: M, M, M)

32. Q: Reaction Quotient Reaction Quotient
Calculated the same as K, but using initial concentrations
3. Q < K shifts to products
Q = K at equilibrium
Q > K shifts to reactants

33. If you introduce 0. 0200 mol of HI, 0. 0100 mol of H2 and 0
If you introduce mol of HI, mol of H2 and mol of I2 in a 2.00 L flask, which way will the reaction proceed to reach equilibrium?
H2(g) + I2(g)  2HI(g) Kc = 51
(Ans: Q = 1.3)

34. 2. Predict which way the following reaction will proceed as it reaches eq. Assume that you start with [SO3] = M, [SO2] = M and [O2] = 0.03M.
2SO3(g)  2SO2(g) + O2(g)
Kc =
(Ans: Q = 0.2)

35. Predict which way the following reaction will proceed as it reaches eq
Predict which way the following reaction will proceed as it reaches eq. Assume that you start with [NH3] = M, [N2] = M and no H2. Kc= 0.105
N2(g) + 3H2(g)  2NH3(g)

36. LeChatelier’s Principle
Blue Bottle Demo 5 grams KOH 3 grams Dextrose 250 mL of water 1 drop methylene blue

37. Le’Chatelier’s Principle
If a system at eq. is disturbed, it will shift to relieve that disturbance
Definition – If a system at eq. Is disturbed, it will shift to relieve that disturbance

41. LiCl(s)  Li+(aq) + Cl-(aq)
N2(g) + 3H2(g)  2NH3(g)
Add N2
Add NH3
Remove NH3 as it forms
Remove H2
N.B. Does NOT apply to solids and liquids. They do not appear in the K.
LiCl(s)  Li+(aq) + Cl-(aq)

42. Disturbing and K Adding products = K increases (TEMPORARILY)
Adding reactants = K decreases (TEMPORARILY)
N2(g) + 3H2(g)  2NH3(g)
Kc = [NH3]2
[N2][H2]3

43. N2(g) + 3H2(g)  2NH3(g)
Identify the # of moles of gas on either side.
Show piston drawing
Increase the volume of the container
Decrease the volume of the container

45. N2(g) + 3H2(g)  2NH3(g) Increase the pressure of the system
Decrease the pressure of the system
Soda example (CO2(aq)  CO2(g))
N.B. Adding a noble or inert gas has no effect on the eq. Pressure change without a volume change.

46. Endothermic Reactions – absorb heat from the surroundings
Heat is added (reactants)
Cooking is an example
DH +
Exothermic Reactions – Release heat
Give off heat (products)
Fire is an example
DH -

47. DH = -206 kJ/mol Heat the system Cool the system
CO(g) + 3H2(g)  CH4(g) + H2O(g)
DH = -206 kJ/mol
Heat the system
Cool the system

48. Catalyst
Examples
a. Enzymes
b. Vitamins
c. Catalytic convertor
3. No effect on the position of equilibrium

49. Example 1
N2O4(g)  2NO2(g)
DH = 58 kJ/mol
Add N2O4
Remove NO2 as it forms
Increase the total pressure
Increase the total volume
Cool the solution
Add a catalyst

50. Example 2. DH = -37 kJ/mol Add PbS Remove SO2 as it forms Add O2
2PbS(s) + 3O2(g)  2PbO(s) + 2SO2(g)
DH = -37 kJ/mol
Add PbS
Remove SO2 as it forms
Add O2
Increase volume
Decrease the pressure
Heat the flask

51. Example 3. Given the following eqn
Example 3. Given the following eqn., how could you promote the formation of PCl3 and Cl2? PCl5(g)  PCl3(g) + Cl2(g) DH = 88 kJ/mol

52. CO(g) + 3H2(g)  CH4(g) + H2O(g)
Example 4.
How could you promote the formation of CH4?
CO(g) + 3H2(g)  CH4(g) + H2O(g)
DH = -206 kJ/mol

53. SINGLE ARROW Reaction goes to completion HCl + NaOH  NaCl + H2O I C End Na+ Cl- H2O

54. Double ARROW Reaction goes to equilibrium (all species present) N2 + 3H2  2NH3 I C Equilibrium N2 H2 K = [NH3]2 ratio NH3 [N2][H2]3

55. HC2H3O2(aq) + H2O(l) ↔ H3O+(aq) + C2H3O2-(aq)

56. Fe3+(aq) + SCN-(aq) ↔ FeSCN2+(aq)

57. Co(H2O)62+(aq) + 4Cl-(aq) + 50 kJ/mol ↔ CoCl42-(aq) + 6H2O(l)
(pink) (blue)

58. NaCl(s) ↔ Na+(aq) + Cl-(aq)

59. [O2]3/[O3]2 1/[Cl2]2
[C2H6]2[O2]/[C2H4]2[H2O]2 [CH4]/[H2]2
[Cl2]2/[HCl]4[O2]
16. a) Products b) Reactants
18. Kc = 858
20a) X 105 b) H2S favored
22a) b) c)
26. Kp = 1/PSO2
Na2O is a solid, no molarity or pressure
28. Kc = 10.5
, Products favored
32. a) M, M, 0.40 M b) 58

60. 38. a) 0.0013(R) b) Reactants c) 1.1 X10-5(P)
atm
42a g I2 b) g SO2
0.13 M
0.011 M
48a M PH3 and BCl3
52 a) increase(P) b) decrease(R) c) decrease(R)
d) decrease(R) e) no change f) decrease(R)
54 a) Endothermic b) more moles of gas in product
56 a) kJ b) exothermic
c) Increase pressure Kp = 24.7 Kc =

61. Take-Home Pretest
1.09 g NaOH
20.4
4352
167
Products
Q = 0.637, moves to products
[H2] = M, [Cl2] = M, [HCl] = M

62. 1.82 = 2m log 1.82 = log 2m log 1.82 = m log 2 0.260 = 0.301 m m = 0.864