1. Energy transformations
Chemical
Equilibrium
Thermodynamics
Energy transformations

3. N2O NO2
Initially forward reaction rapid
As some reacts [N2O4] so rate forward 
Initially Reverse reaction slow
No products
As NO2 forms
 Reverse rate
Eventually rateforward = ratereverse
Equilibrium

5. Reaction Reversibility
Closed system
Equilibrium can be reached from either direction
Independent of whether it starts with “reactants” or “products”
Always have the same composition at equilibrium under same conditions
N2O NO2 

6. Products Reactants Equilibrium N2O4 2 NO2
For given overall system composition
Always reach same equilibrium concentrations
Whether equilibrium is approached from forward or reverse direction

7. If equilibrium is established, concentrations don’t change any more.

12. Each set of equilibrium concentrations
Equilibrium position

13. Check it yourself!

16. Relation between Kp and Kc

17. Learning Check Kc = 11.7 Consider the reaction: 2NO2(g) N2O4(g)
If Kp = for the reaction at 25°C, what is value of Kc at same temperature?
n = nproducts – nreactants = 1 – 2 = –1
Kc = 11.7

18. Interpreting Kp or Kc Means product rich mixture
2SO2(g) + O2(g)  2SO3(g)
Kc = 7.0  1025 at 25 ° C
Reaction goes only ~ halfway
Means reactant rich mixture
H2(g) + Br2(g)  2HBr(g)
Kc = 1.4  10–21 at 25 °C

19. more than phase involved
Concentrations of pure liquids and solids do not change with changing the amounts of these substances.

20. Pure solids and liquids do not appear in the expression for equilibrium constant.

21. Reaction Quotient Q
If Q=K → equilibrium
Q ≠ K → not at equilibrium
tries to reach equilibrium

23. For the synthesis of ammonia at 500oC, the equilibrium constant is 6
For the synthesis of ammonia at 500oC, the equilibrium constant is 6.0×10-2. Predict the direction in which the system will shift to reach equilibrium in each of the following cases:
Q >> K
Q will decrease with time
More reactants, less products
System shifts to the right
Reversed reaction dominates
The amount of N2 and H2 will increase
The amount of NH3 will decrease

24. Your turn!
N2O4 was placed in a flask and allowed to reach equilibrium at a temperature where Kp At equilibrium, the pressure of N2O4 was found to be 2.71 atm. Calculate the equilibrium pressure of NO2(g).
N2O NO2

25. At a certain temperature a 1. 00-L flask initially contained 0
At a certain temperature a 1.00-L flask initially contained mol PCl3(g) and 8.70×10-3 mol PCl5(g). After the system had reached equilibrium, 2.00×10-3 mol Cl2(g) was found in the flask. no
change
neq
ceq
6.70×10-3
0.300
2.00×10-3

26. Carbon monoxide reacts with steam to produce carbon dioxide and hydrogen. At 700 K the equilibrium constant is Calculate the equilibrium concentrations of all species if mol of each component is mixed in a L flask. co
change
ceq
Shift to the right
Q < K
x=0.387 mol/L

27. Assume that the reaction for the formation of gaseous hydrogen fluoride from hydrogen and fluorine has an equilibrium constant of 1.15×10-2 at a certain temperature. In a particular experiment, mol of each component was added to a L flask. Calculate the equilibrium concentrations of all species. co
change
ceq
Shift to the right
Q < K
x=1.528 mol/L

28. Quadratic equation Q > K
3.000 mol H2 and mol F2 are mixed in a L flask. Assume that the equilibrium constant for the synthesis reaction at this temperature is 1.15×10-2. Calculate the equilibrium concentration of each component.
Quadratic equation
Assume that gaseous hydrogen iodide is synthesized from hydrogen gas and iodine vapor at a temperature where the equilibrium constant is 1.00×10-2. Suppose HI at 5.000×10-1 atm, H2 at 1.000×10-2 atm, and I2 at 5.000×10-3 atm are mixed in a L
flask. Calculate the equilibrium pressures of all species.
Q > K

29. 1.0 mol NOCl is placed in a 2.0-L flask, what are the equilibrium concentrations?
change
ceq
x=0.010 mol/L

30. How valid is this approximation?
Approximation justified!!

32. H2 HI I2 I. Concentration Changes
If the conc. of a substance is increased, the equilibrium will shift in a way that will decrease the conc. of the substance that was added.
Where will the reaction shift?
Decrease HI -
forward
Decrease I2 -
backward H2 HI
forward
Increase H2 - I2
Increase HI -
backward

33. Note:
adding/removing a solid/liquid to an equilibrium system will not cause any shift in the position of equilibrium because this doesn’t change their concentration.
addition of an inert gas such as He, Ar, Kr, etc. at constant volume, pressure and temperature does not affect the equilibrium because it doesn’t change the concentrations or partial pressures.
Increase CO2 :
Increase CaO
Decrease CO2
Adding Kr
- backward
- No effect
- forward
- No effect

34. The effect of pressure (volume) on an equilibrium system.
An increase in pressure (decrease in volume) shifts the position of the equilibrium in such a way as to decrease the pressure by decreasing the number of moles of gaseous component.
When the volume is increased (pressure decreased), a net reaction occurs in the direction that produces more moles of gaseous component (increase in system pressure).
Decrease in pressure :
Decrease in volume:
backward
forward

35. Sample Problem 17.12
Predicting the Effect of a Change in Volume (Pressure) on the Equilibrium Position
PROBLEM:
For the following reactions, predict the direction of the reaction if the pressure is increased:
(a) CaCO3(s) CaO(s) + CO2(g)
(b) S(s) + 3F2(g) SF6(g)
(c) Cl2(g) + I2(g) ICl(g)
(a) CO2 is the only gas present. The equilibrium will shift to the direction with less moles of gas. Answer: backward
SOLUTION:
There are more moles of gaseous reactants than products.
Answer: forward
(c) There are an equal number of moles of gases on both sides of the reaction. Answer: no effect

36. Effect of Temperature Changes
 T shifts reaction in direction that absorbs heat (enhances the endothermic change)
 T shifts reaction in direction that produces heat (enhances the exothermic change)
Changes in T change the value K
K depends on T
T of exothermic reaction makes K smaller
More heat (product) forces equilibrium to reactants
T of endothermic reaction makes K larger
More heat (reactant) forces equilibrium to products

38. Effect of Change in Temperature
Ice water
Boiling water
Cu(H2O)42+(aq) + 4Cl–(aq) CuCl42–(aq) + 4H2O
blue yellow
Reaction endothermic
Adding heat shifts equilibrium toward products
Cooling shifts equilibrium toward reactants
Center – system at equilibrium
Fig. 14.7

39. [Co(H2O)6]2+(aq) + 4Cl–(aq) [Co(Cl)4]2–(aq) + 6H2O(ℓ)
Your Turn!
The equilibrium between aqueous cobalt ion and the chlorine ion is shown:
[Co(H2O)6]2+(aq) + 4Cl–(aq) [Co(Cl)4]2–(aq) + 6H2O(ℓ)
pink blue
It is noted that heating a pink sample causes it to turn violet.
The reaction is:
endothermic
exothermic
cannot tell from the given information

40. LE CHATELIER’S PRINCIPLE
STRESS
SHIFT
WHY?
increase concentration of a substance
away from substance
extra concentration needs to be used up
decrease concentration of a substance
towards substance
need to produce more of substance to make up for what was removed
increase pressure of system
towards fewer moles of gas
for gas: pressure increase = volume decrease
decrease pressure of system
towards more moles of gas
for gas: pressure decrease = volume increase
increase temperature of system
away from heat/ energy
exothermic reaction is favored
extra heat/ energy must be used up
decrease temperature of system
towards heat/ energy
exothermic reaction is favored
more heat/ energy needs to be produced to make up for the loss
add a catalyst
NO SHIFT
The rates of both the forward and reverse reactions are increased by the same amount.

41. N2(g) + 3H2(g)  2NH3(g) + 22.0 kcal
10. Decrease press.
9. Increase press.
8. Decrease temp
7. Increase temp
6. Remove NH3
5. Remove H2
4. Remove N2
3. Add NH3
2. Add H2
1. Add N2
[NH3]
[H2]
[N2]
Shift
Stress

42. 2CO2(s) + heat 2CO(s) + O2(g)  
CO2 is added
CO is added
O2 is added
CO is removed
pressure is increased
pressure is decreased
temp. is increased
temp. is decreased
catalyst is added
stress
2CO2(s) + heat 2CO(s) + O2(g)  
Do by hand.

44. Given the reaction: N2(g) + O2(g) + 182.6 kJ  2NO(g) 
DO NOW 
Given the reaction:
N2(g) + O2(g) kJ  2NO(g)
Which change would cause an immediate increase in the rate of the forward reaction?
increasing the concentration of NO(g)
increasing the concentration of N2(g)
decreasing the reaction temperature
decreasing the reaction pressure 

45. Which changes occur when O2(g) is added to the system?
DO NOW 
2POCl3(g) + energy  2PCl3(g) + O2(g) 
Which changes occur when O2(g) is added to the system?
1) The equilibrium shifts right and [PCl3] increases. 2) The equilibrium shifts right and [PCl3] decreases. 3) The equilibrium shifts left and [PCl3] increases. 4) The equilibrium shifts left and [PCl3] decreases

46. 2SO2(g) + O2(g)  2SO3(g) + heat
QUIZ 
2SO2(g) + O2(g)  2SO3(g) + heat 
For each of the following stresses, state in which direction the equilibrium will shift and what will happen to the concentration of SO2. Explain.
concentration of O2 is decreased
pressure is decreased
temperature is decreased
a catalyst is added