CH16_equilibria_2 - Homogeneous reaction/equilibrium All...

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1 Homogeneous reaction/equilibrium All reactants & products in same phase Can mix freely Heterogeneous reaction/equilibrium Reactants & products in different phases Can’t mix freely Solutions are expressed in M
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2 Heterogeneous Equilibria 2NaHCO 3 (s)  Na 2 CO 3 (s) + H 2 O (g) + CO 2 (g) Equilbrium Law = Can write in simpler form For any pure liquid or solid, ratio of moles to volume of substance (M) is constant Ex. 1 mol NaHCO 3 occupies 38.9 cm 3 2 mol NaHCO 3 occupies 77.8 cm 3 2 ) ( 3 2 ) ( 2 ) ( 2 ) ( 3 2 ] [ ] ][ ][ [ s g g s HCO Na CO O H CO Na K = M M 7 . 25 L 0.0389 NaHCO mol 1 3 = = M M 7 . 25 L 0.0778 NaHCO mol 2 3 = =
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3 Heterogeneous Equilibria 2NaHCO 3 (s)  Na 2 CO 3 (s) + H 2 O (g) + CO 2 (g) Ratio (n/V) or molar concentration of NaHCO 3 is constant (25.7 mol/L) regardless of sample size. Likewise can show that molar concentration of Na 2 CO 3 solid is constant regardless of sample size So concentrations of pure solids & liquids can be incorporated into equilibrium constant, K c Equilibrium law for heterogeneous is ] ][ [ ] [ ] [ ) ( 2 ) ( 2 2 ) ( 3 2 ) ( 3 2 g g s s c CO O H HCO Na CO Na K K = =
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4 Learning Check Write equilibrium laws for the following: Ag + (aq) + Cl (aq) AgCl (s) H 3 PO 4 (aq) + H 2 O (l)  H 3 O + (aq) + H 2 PO 4 (aq) 3Ca 2+ (aq) + 2PO 4 3– (aq) Ca 3 (PO 4 ) 2 (s) ] ][Cl [Ag 1 - + = c K ] PO [H ] PO ][H O [H 4 3 4 2 3 - + = c K 2 3 4 3 2 ] [PO ] [Ca 1 - + = c K
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5 Equilibrium Positions & “Shifts” Equilibrium positions Combination of concentrations that allow Q = K Infinite number of possible equilibrium positions Le Châtelier’s principle System at equilibrium ( Q = K ) when upset by disturbance ( Q ≠ K ) will shift to offset stress System said to shift to right when forward reaction is dominant ( Q < K ) System said to “shift to left” when
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6 Q = K reaction at equilibrium Q < K reactants products Too many reactants Must convert some reactant to product to move reaction toward equilibrium Q > K reactants products Too many products Must convert some product to reactant to
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7 Examples of Le Châtelier’s Principle Let’s see how this works with changes in 1. Concentration 2. 3. Temperature 4. Catalysts 5. Adding an inert gas to a system as constant volume
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8 1. Effect of Change in Concentration Cu(H 2 O) 4 2+ (aq) + 4 Cl (aq)  CuCl 4 2– (aq) + 4 H 2 O (l) blue yellow Equilibrium mixture is blue-green Add excess Cl (conc HCl) Equilibrium shifts to products Makes more yellow CuCl 4 2– Solution becomes green 4 ) ( ) ( 2 4 2 4 ) ( 2 ) ( 2 4 ] ][ ) ( [ ] ][ [ aq aq l aq c Cl O H Cu O H CuCl K - + - = 4 ) ( ) ( 2 4 2 ) ( 2 4 4 ) ( 2 ] ][ ) ( [ ] [ ] [ aq aq aq l c c Cl O H Cu CuCl O H K K - + - = =
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9 Effect of Change in Concentration Cu(H 2 O) 4 2+ (aq) + 4 Cl (aq)  CuCl
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This note was uploaded on 04/06/2008 for the course CHEM 1220 taught by Professor Meghee during the Spring '08 term at St. Johns Duplicate.

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CH16_equilibria_2 - Homogeneous reaction/equilibrium All...

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