CHEM 5013 Applied Chemical Principles Chapter Twelve – Chemical Equilibrium Professor Bensley Alfred State College

Chapter Objectives Explain that equilibrium is dynamic and that at equilibrium, the forward and backward reaction rates are equal. State these ideas in your own words. Explain that equilibrium is dynamic and that at equilibrium, the forward and backward reaction rates are equal. State these ideas in your own words. Write the equilibrium constant expression for any reversible reaction. Write the equilibrium constant expression for any reversible reaction. Use LeChatlier’s principle to explain the response of an equilibrium system to an applied stress. Use LeChatlier’s principle to explain the response of an equilibrium system to an applied stress.

Chemical Equilibrium What is chemical equilibrium? What is chemical equilibrium? Example: Example: CO (g) + 3H 2 (g)  CH 4 (g) + H 2 O (g) becomes CO (g) + 3H 2 (g) CH 4 (g) + H 2 O (g)

Forward and Reverse Reactions This photo sequence shows the water level in two glasses over the course of 17 days. The glass on the left is covered. This photo sequence shows the water level in two glasses over the course of 17 days. The glass on the left is covered.

Dynamic Equilibrium CO (g) + 3 H 2 (g) CH 4 (g) + H 2 O (g)

Equilibrium Constant Equilbrium constant = K c = Example: Example: Methanol is made from mixing H 2 and CO at high T and P. 2H 2 (g) + CO (g) CH 3 OH (g) a) Write K c for this reaction. b) Write K c for the reverse reaction.

Homogeneous and Heterogeneous Equilibria Homogeneous equilibria: Heterogeneous equilibria: Example: Write K c expression for the following reaction: CaCO 3 (s) CaO(s) + CO 2 (g)

Using the Equilibrium Constant K c for 2NO (g) + O 2 (g) 2 NO 2 (g) K c for 2NO (g) + O 2 (g) 2 NO 2 (g) is 4.0x10 13 at 25°C. Which side (reactant or product) is favored at equilibrium? is 4.0x10 13 at 25°C. Which side (reactant or product) is favored at equilibrium?

LeChatlier’s Principle You can change the yield of a product in an equilibrium reaction 3 ways: You can change the yield of a product in an equilibrium reaction 3 ways:

LeChatlier’s Principle Change One – Altering concentrations: Change One – Altering concentrations: 2Fe(s) + 3H 2 O (g) Fe 2 O 3 (s) + 3H 2 (g) What happens if I raise [H 2 ]? How do I make the iron oxidize (rust) faster?

Effect of a Change in Pressure on Equilibrium, When Gases Are Present CO 2 (g) + H 2 O (l)H 2 CO 3 (aq) How is soda carbonated? What happens when the can is opened? How does system respond to relieve added stress?

LeChatlier’s Principle Change Two – Altering Gas Pressures Change Two – Altering Gas Pressures Can you increase the amount of product in each of the following rxns. by increasing the pressure? a) CO 2 (g) + H 2 (g) CO(g) + H 2 O (g) b) 4CuO(s) 2Cu 2 O (s) + O 2 (g) c) 2SO 2 (g) + O 2 (g) 2SO 3 (g)

LeChatlier’s Principle Exothermic Reaction: Exothermic Reaction: Endothermic Reaction: Endothermic Reaction:

LeChatlier’s Principle Change Three – Heat of Reaction Change Three – Heat of Reaction How would a temperature increase affect each of the equilibria below? a) AgNO 3 (s) Ag + (aq) + NO 3 - (aq) ∆H 0 = 22.6 kJ/mol b) C(s) + O 2 (g) 2 CO (g) ∆H 0 = -209 kJ/mol