chap15_bch1049_07MCWC1a

chap15_bch1049_07MCWC1a - Chemical Equilibrium (Chapter 15)...

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1 Equilibrium Chemical Equilibrium (Chapter 15) What’s Ahead: 1. 1. Concept of Equilibrium Concept of Equilibrium 2. 2. Equilibrium Constant Equilibrium Constant 3. 3. Calculating and Applying Equilibrium Constants 4. 4. Le Ch âtelier telier ’s Principle Principle Equilibrium Concept: Chemical equilibrium is established when a reaction and its reverse reaction proceed at the same rate (for reversible reactions only). (NO 2 -N 2 O 4 )
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2 Equilibrium Depicting Equilibrium In a system at equilibrium, both the forward and reverse reactions are occurring; as a result, we write its equation with a double arrow: N 2 O 4 ( g ) 2 NO 2 ( g ) Equilibrium The Equilibrium Constant • Forward reaction: N 2 O 4 ( g ) ⎯⎯→ 2 NO 2 ( g ) • Rate law: Rate = k f [N 2 O 4 ] • Reverse reaction: 2 NO 2 ( g ) ⎯⎯→ N 2 O 4 ( g ) • Rate law: Rate = k r [NO 2 ] 2
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3 Equilibrium The Equilibrium Constant The ratio of the rate constants is a constant at given temperature, and the expression becomes: K eq = k f k r [NO 2 ] 2 [N 2 O 4 ] = • Therefore, at equilibrium, Rate f = Rate r k f [N 2 O 4 ] = k r [NO 2 ] 2 Equilibrium The Concept of Equilibrium • As a system tends towards equilibrium, both the forward and reverse reactions occur. • At equilibrium, the rates of the forward and reverse reactions are the same.
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4 Equilibrium A System at Equilibrium • Concentration of reactants change before equilibrium is reached. • Once equilibrium is achieved, the amount of each reactant and product remains constant (but continue to interconvert!); note 2:1 ratio. The Equilibrium Constant • To generalize, consider the reaction: • The equilibrium expression for this reaction would be (subscript c for concentrations in M ): K c = [D] d [E] e [A] a [B] b a A + b B d D + e E Note: K c depends only on the reaction stoichiometry and temperature, not the mechanism.
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5 Equilibrium
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This note was uploaded on 01/11/2011 for the course BCH 1049 taught by Professor Michaelcwchan during the Spring '06 term at City University of Hong Kong.

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chap15_bch1049_07MCWC1a - Chemical Equilibrium (Chapter 15)...

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