chap15_bch1049_07MCWC2b

chap15_bch1049_07MCWC2b - 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 Rate Laws A rate law shows the relationship between the reaction rate and the concentrations of reactants. The exponents ( m and n ) give the order of the reaction with respect to each reactant. The overall reaction order is the sum of the exponents on the reactants in the rate law. This reaction is second-order overall. Although m and n are often same as coefficients in balanced equation, the rate law , plus m and n , must be determined experimentally. a A + b B c C + d D Rate = k [A] m [B] n This reaction is: first order in [NH 4 + ] and first order in [NO 2 ]. Rate = k [NH 4 + ] [NO 2 ] NH 4 + ( aq ) + NO 2 ( aq ) N 2 ( g ) + 2 H 2 O( l ) 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
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4 Equilibrium The Concept of Equilibrium • As a system tends towards equilibrium, both the forward and reverse reactions occur. • At equilibrium, the rates
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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_07MCWC2b - Chemical Equilibrium (Chapter 15)...

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