Chemical Equilibrium Green/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 N 2 (g) + 3H 2 (g) 2NH 3 (g) Add NH 3 Equilibrium shifts left to offset stress 14.5

Le Châtelier’s Principle Changes in Concentration continued ChangeShifts 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 left 14.5 aA + bB cC + dD Add Remove

Le Châtelier’s Principle Changes in Volume and Pressure A (g) + B (g) C (g) ChangeShifts the Equilibrium Increase pressureSide with fewest moles of gas Decrease pressureSide with most moles of gas Decrease volume Increase volumeSide with most moles of gas Side with fewest moles of gas 14.5

Le Châtelier’s Principle Changes in Temperature 14.5 colder hotter Is this reaction exothermic or endothermic? N 2 O 4 (g) + heat 2NO 2 (g) colorless brown

Le Châtelier’s Principle Changes in Temperature ChangeEndothermic Rx Increase temperatureProducts favored Decrease temperatureReactants favored Exothermic Rx Reactants favored Products favored 14.5

uncatalyzedcatalyzed 14.5 Catalyst lowers E a 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

ChangeShift Equilibrium Change Equilibrium Constant Concentrationyesno Pressureyesno Volumeyesno Temperatureyes Catalystno 14.5

Chemistry In Action: The Haber Process N 2 (g) + 3H 2 (g) 2NH 3 (g)  H 0 = kJ/mol Production of Ammonia: What is ammonia used for? What factors might influence this reaction?

Chemistry In Action: The Haber Process N 2 (g) + 3H 2 (g) 2NH 3 (g)  H 0 = kJ/mol

Chemistry In Action: The Haber Process N 2 (g) + 3H 2 (g) 2NH 3 (g)  H 0 = 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) + O 2 (g) SO 2 (g) Production of Sulfuric Acid: What is sulfuric acid used for? What factors might influence the reaction in Step 2? Step 3: SO 3 (g) + H 2 O (l) H 2 SO 4 (l) Step 2: 2 SO 2 (g) + O 2 (g) 2 SO 3 (g)  H 0 = -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 SO 2 (g) + O 2 (g) 2 SO 3 (g)  H 0 = -196 kJ/mol

Haber Process Contact Process

7.2 Homework Read Section 7.2 pp Do Ex 7.2 on p # 2, 3, 4, 6, 7, 10, and two of the following: 11, 12, 13, 14 Due: ____________________