Lecture_overheads_-_Ch06

Lecture_overheads_-_Ch06 - CHEM 321 Quantitative Analysis...

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CHEM 321 – Quantitative Analysis Ch. 6 – Chemical Equilibrium 6-1 Equilibrium Constant K eq 6-2 Equilibrium and Thermodynamics K sp , G 6-3 Solubility Product K sp 6-4 Complex Formation K f , β 6-5 Acids and Bases K a , K b 6-6 pH K w 6-7 Strengths of Acids and Bases
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6-1 Equilibrium Constant For generic reaction a A + b B = c C + d D Equilibrium constant is [ ] [ ] [ ] [ ] b a d c K B A D C eq = Upper case letters (A, B, C, D) are chemical species in the reaction Lower case letters ( a, b, c, d ) are stoichiometric coefficients
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Example Al 3+ + 2Cl - = AlCl 2 + [ ] [ ][ ] 2 - 3 2 eq Cl Al AlCl + + = K Units of concentration used in K expressions: Solutes M (mol/L) Solids unity (in their standard state) Pure compounds unity (in their standard state) Gases atm (standard state = 1 bar = 10 5 Pa = 1 atm) In reality, all equilibrium constants are dimensionless and unitless, as all species’ concentrations are relative to the “standard state” Concentrations of pure/solid substances do not appear in K expressions! Example H 2 O = H + + OH - [H 2 O] does not appear in K [ ][ ] - + = OH H K eq
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Manipulating Equilibrium Constants K forward = 1 / K reverse H 2 O = H + + OH - K for = K w = [H + ][OH - ] H + + OH - = H 2 O K rev = 1 / ([H + ][OH - ]) = 1 / K for When adding 2 equilibria, multiply K’s HA = H + + A - K 1 H + + C = CH + K 2 ----------------------------------------------------------- HA + C = A - + CH + K 3 = (K 1 × K 2 ) Later on, we’ll show that K w = K a K b [ ][ ] [ ] [ ] [ ] [ ] [ ][ ] [ ][ ] C HA CH A C H CH HA A H 2 1 3 + - + + - + = = × = K K K
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Equilibrium and Thermodynamics Enthalpy ( H ) is a measure of heat of reaction H < 0 , reaction is exothermic and gives off heat H > 0 , reaction is endothermic and consumes heat Entropy ( S ) is a measure of disorder of reaction S > 0 , reaction involves more disorder Example dissolving crystal into solution S < 0
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Lecture_overheads_-_Ch06 - CHEM 321 Quantitative Analysis...

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