CHM1311 - Lecture(10)

CHM1311 - Lecture(10) - Chemical Equilibrium Petrucci, Ch....

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1 Chemical Equilibrium Chemical Equilibrium Petrucci, Ch. 15 Petrucci, Ch. 15
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2 Reversible Reactions Reversible Reactions So far we have considered reactions that proceed in one direction. A B For many reactions the reverse process is theoretically possible. B A Many reactions move in both directions (they are REVERSIBLE). A B A reversible reaction is represented by a bi-directional arrow:
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Example of irreversible reaction
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Examples of reversible chemical reactions
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Environmental Calcium Carbonate Environmental Calcium Carbonate Chemistry Chemistry Slow dissolution of limestone in mildly acidic groundwater results in formation of caves. When water evaporates, the reverse reaction occurs and CaCO 3 is regenerated. Stalactites and stalagmites are formed this way. CaCO 3 (s) + CO 2 (aq) + H 2 O (l) Ca(HCO 3 ) 2 (aq) K eq = 2.6 x 10 -5
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6 Reversible Reactions Reversible Reactions Upon heating the solution, the solid PbCl 2 dissolves and the aqueous ions are regenerated. PbCl 2 (s) Pb 2+ (aq) + 2 Cl - (aq) Pb 2+ (aq) + 2 Cl - (aq) PbCl 2 (s) When aqueous solutions of Pb 2+ and Cl - are combined, solid PbCl 2 precipitate is formed.
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7 The reversible reaction is represented with a bi-directional arrow . Pb 2+ (aq) + 2Cl - (aq) PbCl 2 (s) The forward arrow represents the precipitation reaction The reverse arrow represents the dissolution reaction Reversible Reactions Reversible Reactions
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8 Reversible Reactions Reversible Reactions Co(H Co(H O) O) Cl Cl Co(H Co(H 2 2 O) O) 4 4 Cl Cl 2 2 + 2 H + 2 H 2 O O PINK PINK BLUE BLUE Add heat Cool When products and reactants are different colors, the reversibility of a reaction can be observed by observing the color change.
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9 Properties of Equilibrium Properties of Equilibrium 1) 1) 1) A reversible reaction is said to be in EQUILIBRIUM if: Not all reversible reactions are in a state of equilibrium!
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Static/dynamic equilibria
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11 Phase Changes are Equilibrium Processes Phase Changes are Equilibrium Processes H 2 O (s) H 2 O (l) In the solid-liquid equilibrium (at 0 o C), one molecule of solid is converted to liquid for every one molecule of liquid that is converted to solid.
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12 The Equilibrium Constant, K The Equilibrium Constant, K A generic reversible reaction is represented below: a A + b B c C + d D (where a, b, c, and d are the stoichiometric coefficients) The Law of Mass Action The Law of Mass Action If a reversible reaction is in equilibrium at a given temperature, then the ratio of concentrations of products to concentrations of reactants, each raised to the power of their stoichiometric coefficients, is a constant a constant . The constant is called the EQUILIBRIUM CONSTANT, K EQUILIBRIUM CONSTANT, K :
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13 H 2 CO CH 4 = H 2 O time moles of substance 0 1 2 3 Which of the following statements is correct? 1. At equilibrium the reaction stops.
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This note was uploaded on 01/17/2010 for the course CHM BIO1130 taught by Professor Houseman during the Fall '09 term at University of Ottawa.

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CHM1311 - Lecture(10) - Chemical Equilibrium Petrucci, Ch....

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