1. Chemical Equilibrium

2. Objectives Define key terms and concepts.
Express the equilibrium constant for a reaction.
Calculate the equilibrium constant for a reaction.
Determine how chemical equilibrium is effected by temperature, concentration, pressure, volume, and catalysts.
Predict how the equilibrium of a chemical reaction will shift using LeChâtelier’s Principle.

3. Chemical Equilibrium Equilibrium
a state in which there are no observable changes as time goes by.
The rate of the reaction can be determined for both the forward the reverse reactions.
Chemical Equilibrium
When the rates of the forward and reverse reaction are equal
The concentration of the reactants and products in solution no longer change.
Crash Course Equilibrium
Physical equilibrium
H2O (l)
H2O (g)
Chemical equilibrium
N2O4 (g)
2NO2 (g)

4. Chemical Equilibrium Equilibrium Constant aA + bB cC + dD
Rates the concentrations of reactants and product as equilibrium
aA + bB cC + dD
[C]c[D]d
[A]a[B]b
K =

5. Expressing Equilibrium Constants
Homogeneous Equilibrium
Reactants and products are in the same phase
Heterogeneous Equilibrium
Reactants and products are in different phases
Kc is the equilibrium constant expressed in terms of concentration.
If Kc is large, the equilibrium mixture contains mostly products
If Kc is small, the equilibrium mixture contains mostly reactants
If Kc is about 1, the equilibrium contains similar amounts of reactants and products

6. Rules for Writing Equilibrium Constant Expressions - Kc
The chemicals involved in the reaction can be expressed in moles/L for liquids, or in moles/L or atmospheres for gasses.
The concentrations of pure solids or liquids (in heterogeneous equilibria) and solvents (in homogeneous equilibria) do not appear in the equilibrium constant expressions.
The equilibrium constant is unit less.
In quoting a value for the equilibrium constant, the balanced equation and temperature must be specified.

7. Rules for Writing Equilibrium Constant Expressions - Kp
Kp is the equilibrium constant expressed in terms of the partial pressures of the gases being reacted.
Where ∆n = ∑nproducts - ∑nreactants for gases only
R= L•atm/mole•K
Kp = Kc(RT)∆n

8. does not depend on the amount of CaCO3 or CaO
CaCO3 (s) CaO (s) + CO2 (g)
PCO 2
= Kp
PCO 2
does not depend on the amount of CaCO3 or CaO

9. Calcium oxide is prepared by heating a source of calcium carbonate (such as limestone or seashells) CaCO3(s) CaO(s) + CO2(g) What is the equilibrium constant expression, Kc, for the reaction?

10. The Mond process for purifying nickel involves the formation of nickel tetracarbonyl, Ni(CO)4, from nickel and carbon monoxide Ni(s) + CO(g) Ni(CO)4(g) What is the equilibrium constant expression, Kc, for the reaction?

11. Write the expression for the equilibrium constant for the following reaction: H2(g) + O2(g) H2O(g) What would the equilibrium constant , Kc, be for the reverse reaction?

12. Write the expression for the equilibrium constant for the following reaction: CO(g) + H2(g) CH4(g) + H2O(g) What would the equilibrium constant, Kc, be for the reverse reaction?

13. Determine the equilibrium constant (Kc and Kp) for the following reaction CO(g) + H2(g) CH4(g) + H2O(g) if at equilibrium 0.613mole of CO, 1.839mole hydrogen gas, 0.387mole methane, and 0.387moles water are contained in a 10.0L reaction vessel at 600K.

14. HI decomposes according to the equation HI(g) H2(g) + I2(g) When 4
HI decomposes according to the equation HI(g) H2(g) + I2(g) When 4.0moles of HI was placed in a 5L vessel at 731K, the equilibrium mixture was found to contain 0.442mole iodine and hydrogen gas. What is the values of Kc and Kp for the decomposition of HI at this temperature?

15. If Kc for the following reaction is 2
If Kc for the following reaction is 2.5x10-8 HI(g) H2(g) + I2(g) Does the equilibrium mixture contain mostly reactant or products? If the concentration of hydrogen gas and iodine are1.25x10-6M at equilibrium, what is the equilibrium concentration of HI?

16. The equilibrium constant Kc for the reaction NO(g) + O2(g) NO2(g) Equals 4.0x1013 at 298K. Does the equilibrium mixture contain mostly reactant or products? If the concentration of NO and oxygen gas is 2.0x10-6M at equilibrium, what is the equilibrium concentration of NO2?

17. What are Your Questions?

18. Predicting the Direction of a Reaction
Reactant Quotient (Qc)
Obtained by substituting the initial concentrations into the equilibrium constant expression
By comparing Qc to Kc, the direction of the reaction can be determined.
Qc < Kc, the reaction shifts towards the products
Qc > Kc, the reaction shifts towards the reactants
Qc = Kc, the system is at equilibrium

19. Hydrogen gas reacts with nitrogen gas to produce ammonia gas. If a 50
Hydrogen gas reacts with nitrogen gas to produce ammonia gas. If a 50.0L reaction vessel contains 1.0mole of nitrogen gas, 3.0mole of hydrogen gas, and 0.50mole ammonia. Which direction will the reaction go to reach equilibrium at 673K if Kc for the reaction is 0.50?

20. Carbon dioxide gas will react with solid carbon to produce carbon monoxide gas. A10.0L vessel contain mole of carbon dioxide and 0.10mole carbon monoxide. A small amount of carbon is added to the vessel and the temperature raised to 1373K. What will happen to the reaction? The value of Kc for this reaction is 1.17 at 1373K. Assume the volume of the gas is equal to the volume of the container.

21. Hydrogen gas reacts with oxygen gas to produce water vapor. If a 40
Hydrogen gas reacts with oxygen gas to produce water vapor. If a 40.0L reaction vessel contains 5.9g of hydrogen gas, 8.1g of oxygen gas, and 6.5g water vapor. Which direction will the reaction go to reach equilibrium at 700K if Kc for the reaction is 0.85?

22. Calculating Equilibrium Concentrations
Express all concentrations in a reaction in terms of the initial concentration and the unknown quantity x, representing the change in concentration.
Write the equilibrium constant expression in terms of the equilibrium concentrations. Solve for x.
Calculate the equilibrium concentration of all species.

23. A gaseous mixture contains 0. 30mole CO, 0. 10mole hydrogen gas, and 0
A gaseous mixture contains 0.30mole CO, 0.10mole hydrogen gas, and 0.20mole water along with an unknown amount of methane in each liter. The reaction occurs according to the following reaction: CO(g) + 3H2(g) CH4(g) + H2O(g) Calculate the concentration of methane in this mixture? Kc for the reaction is 3.92.

24. Phosphorus pentachloride gives an equilibrium mixture of PCl5, PCl3, and Cl2 when heated. PCl5(g) PCl3(g) + Cl2(g) A 1.0L vessel contains an unknown amount of PCl5 and 0.020mole each of PCl3 and Cl2 at equilibrium at 523K. How many moles of phosphorus pentachloride are in the vessel if Kc for the reaction is at 523K?

25. The reaction CO(g) + H2O(g) CO2(g) + H2(g) Is used to increase the ratio of hydrogen in synthesis gas (mixtures of CO and H2). If you start with 1.0mole of each of CO and water in a 50.0L vessel, how many moles of each substance are in the equilibrium mixture at 1,273K? Kc for the reaction is 0.58 at 1,273?

26. What is the equilibrium composition of a reaction mixture if you start with 0.50mole each of hydrogen gas and iodine in a 1.0L vessel? HI(g) H2(g) + I2(g) Kc for the reaction at 731K is 49.7.

27. If 1. 0mole of hydrogen gas and 2. 0mole of iodine are placed in a 1
If 1.0mole of hydrogen gas and 2.0mole of iodine are placed in a 1.0L container, how many moles of substances are in the gaseous mixture when it comes to equilibrium at 731K? HI(g) H2(g) + I2(g) Kc for the reaction at 731K is 49.7.

28. What are Your Questions?

29. Factors that Affect Chemical Equilibrium
LeChâtelier’s Principle
States that if an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as it tries to reestablish equilibrium.
Factors that Affect Chemical Equilibrium
Concentration
Temperature
Pressure and Volume
Catalysts
Applying the Concepts of Equilibrium

30. CoCl2•6H2O + HCl ↔ CoCl42- + 6H2O

31. FeCl3 + KSCN ↔ KCl + Fe(SCN)2

32. CO(g) + H2O(g) CO2(g) + H2(g)
Which direction will the reactions shift to if hydrogen gas is added to the following reactions:
H2(g) + I2(g) HI(g)
CO(g) + H2O(g) CO2(g) + H2(g)
2H2S(g) H2(g) + S2(g)
Which direction will the following reactions shift if the pressure is increased by decreasing the volume?
C(s) + S2(g) CS2(g)
CO(g) + Cl2(g) COCl2(g)

33. CO(g) + H2O(g) CO2(g) + H2(g) ΔH = -263kJ
Which direction will the following reactions shift if the temperature of the reaction is increased?
H2(g) + I2(g) HI(g) ΔH = 51.8kJ
CO(g) + H2O(g) CO2(g) + H2(g) ΔH = -263kJ
C(s) + S2(g) + heat CS2(g)
CO(g) + Cl2(g) COCl2(g) ΔH = 75.2kJ
2H2S(g) H2(g) + S2(g) + heat
Which direction will each of the reactions listed above shift if a catalyst is used?

34. What are Your Questions?