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Chemical EquilibriumGreen/Damji – Chapter 7.2
Chang - Chapter 14
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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
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