Chemical EquilibriumGreen/Damji – Chapter 7.2

Chang - Chapter 14

Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

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 the system reaches a new equilibrium position.

Le Châtelier’s Principle

• Changes in Concentration

N2 (g) + 3H2 (g) 2NH3 (g)

AddNH3

Equilibrium shifts left to offset stress

14.5

Le Châtelier’s Principle

• Changes in Concentration continued

Change Shifts the Equilibrium

Increase concentration of product(s) left

Decrease concentration of product(s) right

Decrease concentration of reactant(s)

Increase concentration of reactant(s) right

left14.5

aA + bB cC + dD

AddAddRemove Remove

Le Châtelier’s Principle

• Changes in Volume and Pressure

A (g) + B (g) C (g)

Change Shifts the Equilibrium

Increase pressure Side with fewest moles of gas

Decrease pressure Side with most moles of gas

Decrease volume

Increase volume Side with most moles of gas

Side with fewest moles of gas

14.5

Le Châtelier’s Principle

• Changes in Temperature

14.5colder hotter

Is this reaction exothermic or endothermic?

N2O4 (g) + heat 2NO2 (g)

colorless brown

Le Châtelier’s Principle

• Changes in Temperature

Change Endothermic Rx

Increase temperature Products favored

Decrease temperature Reactants favored

Exothermic Rx

Reactants favored

Products favored

14.5

uncatalyzed catalyzed

14.5

Catalyst lowers Ea for both forward and reverse reactions.

Catalyst does not change equilibrium constant or shift equilibrium.

• Adding a Catalyst• does not change K• does not shift the position of an equilibrium system• system will reach equilibrium sooner

Le Châtelier’s Principle

Le Châtelier’s Principle

Change Shift EquilibriumChange Equilibrium

Constant

Concentration yes no

Pressure yes no

Volume yes no

Temperature yes yes

Catalyst no no

14.5

Chemistry In Action: The Haber Process

N2 (g) + 3H2 (g) 2NH3 (g) DH0 = -92.6 kJ/mol

Production of Ammonia:

What is ammonia used for?

What factors might influence this reaction?

Chemistry In Action: The Haber Process

N2 (g) + 3H2 (g) 2NH3 (g) DH0 = -92.6 kJ/mol

Chemistry In Action: The Haber Process

N2 (g) + 3H2 (g) 2NH3 (g) DH0 = -92.6 kJ/mol

Production of Ammonia:

What specific conditions are used industrially to maximize the yield of ammonia in a cost effective way?

(1) ? Temp ?

(2) ? Pressure ?

(3) ? Equilibrium ?

Chemistry In Action: The Contact Process

Step 1: S (s) + O2 (g) SO2 (g)

Production of Sulfuric Acid:

What is sulfuric acid used for?

What factors might influence the reaction in Step 2?

Step 3: SO3 (g) + H2O (l) H2SO4 (l)

Step 2: 2 SO2 (g) + O2 (g) 2 SO3 (g) DH0 = -196 kJ/mol

Chemistry In Action: The Contact Process

Step 2 in the Production of Sulfuric Acid :

What specific conditions are used industrially to maximize the yield of sulfuric acid in a cost effective way?

(1) ? Temp ?

(2) ? Pressure ?

(3) ? Catalyst ?

Step 2: 2 SO2 (g) + O2 (g) 2 SO3 (g) DH0 = -196 kJ/mol

Haber Process Contact Process

7.2 Homework

Read Section 7.2 pp 185-190

Do Ex 7.2 on p 190-192

# 2, 3, 4, 6, 7, 10, and two of the following: 11, 12, 13, 14

Due: ____________________