CHAPTER_13_notes - 2/8/2009 Chemical Equilibrium CHAPTER 13...

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2/8/2009 1 CHAPTER 13 Chemical Equilibrium The Equilibrium State Chemical Equilibrium : The state reached when the concentrations of reactants and products remain constant over time. 2NO 2 ( g ) N 2 O 4 ( ) Brown Colorless The Equilibrium State 2NO 2 ( ) N 2 O 4 ( ) Chemical Equilibrium Chemical Equilibrium In both experiments, a state of equilibrium is reached when the the concentrations level off at constant values: [N 2 O 4 ] = 0.0337M ; [NO 2 ] = 0.0125M Reaction Rate Time Rate of reverse reaction: N 2 O 4 NO 2 Rate of forward reaction: N 2 O 4 NO 2 At Equilibrium: Rate Forward Reaction = Rate Reverse Reaction 2NO 2 ( ) N 2 O 4 ( )
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2/8/2009 2 The Equilibrium Constant K c c C + d D a A + b B For a general reversible reaction: Equilibrium constant Equilibrium equation : Products Reactants [A] a [B] b [C] c [D] d K c = Equilibrium constant expression For the following reaction: 2NO 2 ( g ) N 2 O 4 ( ) = 4.64 x 10 -3 (at 25 °C) [N 2 O 4 ] [NO 2 ] 2 K c = The Equilibrium Constant K c = 4.63 x 10 -3 0.0429 (0.0141) 2 [N 2 O 4 ] [NO 2 ] 2 K c = = 4.64 x 10 -3 0.0337 (0.0125) 2 Experiment 1 Experiment 5 The Equilibrium Constant K c The Equilibrium Constant and the Equilibrium Constant Expression are for the chemical equation as Written. Examples: 2NH 3 ( ) N 2 ( ) + 3H 2 ( ) N 2 ( ) + 3H 2 ( ) 2NH 3 ( ) 4NH 3 ( ) 2N 2 ( ) + 6H 2 ( ) [N 2 ][H 2 ] 3 [NH 3 ] 2 K c = K c [N 2 ][H 2 ] 3 [NH 3 ] 2 = = K c 1 = [N 2 ] 2 [H 2 ] 6 [NH 3 ] 4 ’’ K c = K c 2 The Equilibrium Constant K c P is the partial pressure of that component 2NO 2 ( ) N 2 O 4 ( ) K p = N 2 O 4 P 2 NO 2 P
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2/8/2009 3 The Equilibrium Constant K P K p = K c (RT) D n 0.082058 K mol L atm R is the gas constant: T is the absolute temperature (Kelvin). D n = (Number of moles of gaseous Products) - (Number of moles of gaseous Reactants) Heterogeneous Equilibria CaO( s ) + CO 2 ( g ) CaCO 3 ( ) Lime Limestone (1) (1)[CO 2 ] = Pure solids and pure liquids are not included. [CaCO
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CHAPTER_13_notes - 2/8/2009 Chemical Equilibrium CHAPTER 13...

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