CHEM 5013 CHEM 5013 Applied Chemical Applied Chemical

PrinciplesPrinciples

Chapter Twelve – Chemical Chapter Twelve – Chemical EquilibriumEquilibrium

Professor BensleyProfessor BensleyAlfred State CollegeAlfred State College

Chapter ObjectivesChapter Objectives

Explain that equilibrium is dynamic and Explain that equilibrium is dynamic and that at equilibrium, the forward and that at equilibrium, the forward and backward reaction rates are equal. State backward reaction rates are equal. State these ideas in your own words.these ideas in your own words.

Write the equilibrium constant expression Write the equilibrium constant expression for any reversible reaction.for any reversible reaction.

Use LeChatlier’s principle to explain the Use LeChatlier’s principle to explain the response of an equilibrium system to an response of an equilibrium system to an applied stress.applied stress.

Chemical EquilibriumChemical Equilibrium

What is What is chemical equilibriumchemical equilibrium?? Example:Example:

CO (g) + 3HCO (g) + 3H22 (g) (g) CHCH44(g) + H(g) + H22O O (g)(g)

becomesbecomes

CO (g) + 3HCO (g) + 3H22 (g) CH (g) CH44(g) + H(g) + H22O O (g)(g)

Forward and Reverse Forward and Reverse ReactionsReactions

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

Dynamic EquilibriumDynamic Equilibrium

CO (g) + 3 H2 (g) CH4(g) + H2O (g)

Equilibrium ConstantEquilibrium Constant Equilbrium constant = Kc =

Example:Example:

Methanol is made from mixing HMethanol is made from mixing H22 and CO at high T and P. and CO at high T and P.

2H2H22 (g) + CO (g) (g) + CO (g) CH CH33OH (g)OH (g)

a) Write Ka) Write Kcc for this reaction. for this reaction.

b) Write Kb) Write Kcc for the reverse reaction. for the reverse reaction.

Homogeneous and Homogeneous and Heterogeneous EquilibriaHeterogeneous Equilibria

Homogeneous equilibria:

Heterogeneous equilibria:

Example: Write KExample: Write Kcc expression for expression for the following the following reaction: CaCOreaction: CaCO33 (s) (s) CaO(s) + COCaO(s) + CO22 (g) (g)

Using the Equilibrium Using the Equilibrium ConstantConstant

KKcc for 2NO (g) + O for 2NO (g) + O22(g) 2 NO(g) 2 NO22 (g) (g)

is 4.0x10is 4.0x101313 at 25 at 25°C. Which side °C. Which side (reactant or product) is favored at (reactant or product) is favored at equilibrium?equilibrium?

LeChatlier’s PrincipleLeChatlier’s Principle You can change the yield of a product You can change the yield of a product

in an equilibrium reaction 3 ways:in an equilibrium reaction 3 ways:1.1.

2.2.

3.3.

LeChatlier’s PrincipleLeChatlier’s Principle

Change One – Altering concentrations:Change One – Altering concentrations:

2Fe(s) + 3H2Fe(s) + 3H22O (g) FeO (g) Fe22OO33(s) + 3H(s) + 3H22 (g) (g)

What happens if I raise [HWhat happens if I raise [H22]?]?

How do I make the iron oxidize (rust) How do I make the iron oxidize (rust) faster?faster?

Effect of a Change in Effect of a Change in Pressure on Equilibrium, Pressure on Equilibrium, When Gases Are PresentWhen Gases Are Present

COCO22 (g) + H (g) + H22O (l)O (l) HH22COCO33 (aq) (aq)

How is soda carbonated? What happens when the

can is opened?How does system respond to relieve added

stress?

LeChatlier’s PrincipleLeChatlier’s Principle

Change Two – Altering Gas PressuresChange Two – Altering Gas Pressures

Can you increase the amount of product Can you increase the amount of product in each of the following rxns. by in each of the following rxns. by increasing the pressure?increasing the pressure?

a) COa) CO22 (g) + H (g) + H22 (g) CO(g) + H (g) CO(g) + H22O (g)O (g)

b) 4CuO(s) 2Cub) 4CuO(s) 2Cu22O (s) + OO (s) + O22 (g) (g)

c) 2SOc) 2SO22 (g) + O (g) + O22 (g) 2SO (g) 2SO33 (g) (g)

LeChatlier’s PrincipleLeChatlier’s Principle

Exothermic Reaction:Exothermic Reaction:

Endothermic Reaction:Endothermic Reaction:

LeChatlier’s PrincipleLeChatlier’s Principle

Change Three – Heat of ReactionChange Three – Heat of ReactionHow would a temperature increase affect each of the equilibria below?a) AgNO3 (s) Ag+ (aq) + NO3

- (aq)

∆H0 = 22.6 kJ/mol

b) C(s) + O2 (g) 2 CO (g)

∆H0 = -209 kJ/mol