1. Chapter Thirteen:
CHEMICAL EQUILIBRIUM

2. The Equilibrium Condition

3. Chemical Equilibrium
The state where the concentrations of all reactants and products remain constant with time.
On the molecular level, there is frantic activity. Equilibrium is not static, but is a highly dynamic situation.
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4. Equilibrium Is: Macroscopically static. Microscopically dynamic
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5. Changes in Concentration
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6. The Changes with Time in the Rates of Forward and Reverse Reactions
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7. React 1
Consider an equilibrium mixture in a closed vessel reacting according to the equation
H2O(g) + CO(g) H2(g) + CO2(g)
You add more H2O to the flask. How does the concentration of each chemical compare to its original concentration after equilibrium is reestablished? Justify your answer.
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8. React 2
Consider an equilibrium mixture in a closed vessel reacting according to the equation
H2O(g) + CO(g) H2(g) + CO2(g)
You add more H2 to the flask. How does the concentration of each chemical compare to its original concentration after equilibrium is reestablished? Justify your answer.
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9. The Ammonia Synthesis Equilibrium
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10. The Equilibrium Constant and Applications

11. The Equilibrium Constant
jA + kB lC + mD k j m l
[B]
[A]
[D]
[C] K =
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12. + React 3 Consider the reaction: K=25
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13. + React 3 reaction on the previous slide.
A set of initial conditions for the
reaction on the previous slide. +
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14. React 3
Draw a quantitative molecular picture that shows what this system looks like after the reactants are mixed and the system reaches equilibrium.
Support your answer with calculations.
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15. React 4 Consider the reaction represented by the equation
Fe3+(aq) + SCN-(aq) FeSCN2+(aq)
Trial #1
6.00 M Fe3+(aq) and 10.0 M SCN-(aq) are mixed and at equilibrium the concentration of FeSCN2+(aq) is 4.00 M.
What is the value for the equilibrium constant for this reaction?
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16. React 4 Fe3+(aq) + SCN-(aq) FeSCN2+(aq) Initial 6.00 10.00 0.00
Change
Equilibrium
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17. React 5 Consider the reaction represented by the equation
Fe3+(aq) + SCN-(aq) FeSCN2+(aq)
Trial #2:
Initial: 10.0 M Fe3+(aq) and 8.00 M SCN−(aq)
Equilibrium: M FeSCN2+(aq) 
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18. React 5 Consider the reaction represented by the equation
Fe3+(aq) + SCN-(aq) FeSCN2+(aq)
Trial #3:
Initial: 6.00 M Fe3+(aq) and 6.00 M SCN−(aq)
Equilibrium: M FeSCN2+(aq)
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19. React 6 Consider the reaction represented by the equation
Fe3+(aq) + SCN-(aq) FeSCN2+(aq)
Fe SCN- FeSCN2+
Trial # M 5.00 M 1.00 M
Trial # M 2.00 M 5.00 M
Trial # M 9.00 M 6.00 M
Find the equilibrium concentrations for all species.
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20. React 7
A 2.0 mol sample of ammonia is introduced into a 1.00 L container. At a certain temperature, the ammonia partially dissociates according to the equation
NH3(g) N2(g) + H2(g)
At equilibrium 1.00 mol of ammonia remains.
Calculate the value for K.
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21. Calculate the equilibrium concentrations of N2O4(g) and NO2(g).
React 8
A 1.00 mol sample of N2O4(g) is placed in a 10.0 L vessel and allowed to reach equilibrium according to the equation
N2O4(g) NO2(g)
K = 4.00 x 10-4
Calculate the equilibrium concentrations of N2O4(g) and NO2(g).
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22. LeChâtelier’s Principle

23. Le Châtelier’s Principle
If a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change.
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24. Effects of Changes on the System
Concentration: The system will shift away from the added component.
2. Temperature: K will change depending upon the temperature (treat the energy change as a reactant).
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25. Effects of Changes on the System
Pressure:
Addition of inert gas does not affect the equilibrium position.
Decreasing the volume shifts the equilibrium toward the side with fewer moles.
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26. LeChâtelier’s Principle
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27. Equilibrium Decomposition of N2O4
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