15 - GENERAL CHEMISTRY Principles and Modern Applications...

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1 TENTH EDITION GENERAL CHEMISTRY Principles and Modern Applications ETRUCCI HERRING MADURA BISSONNETTE PETRUCCI HERRING MADURA BISSONNETTE Principles of Chemical Equilibrium 15 Reaction Mixtures in Dynamic Chemical Equilibrium Reversible Reactions O(l) H (g) CO (s) CaCO (aq) HCO 2 (aq) Ca 2 2 3 - 3 2 Reaction Mixtures in Dynamic Chemical Equilibrium Reversible Reactions O(l) H (g) CO (s) CaCO (aq) HCO 2 (aq) Ca 2 2 3 - 3 2 Reaction Mixtures in Dynamic Chemical Equilibrium Reversible Reactions Reversible chemical reactions can go in either direction, epending on the conditions depending on the conditions. Dynamic chemical equilibrium: a state in which the opposite reactions occur at equal rates so that there is no change of concentrations of species. O(l) H (g) CO (s) CaCO (aq) HCO 2 (aq) Ca 2 2 3 - 3 2 Net Reaction The change of concentrations of species due to unequal rates of the reactions in opposite directions, when the system is not at equilibrium.
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2 The Reaction Quotient and the Equilibrium Constant Reaction Quotient (Q) For a reaction represented by a A + b B c C + d D EXAMPLE : Reaction between hydrogen and iodine gases at 425 ° C to produce hydrogen iodide gas   b a d c B A D C Q 2 2 2 I H HI Q H 2 (g) + I 2 (g) 2HI (g) Initial ( mol L -1 ) 0.0175 0.0175 0 0 Concentration at time 1 (mol L -1 ) 0.0150 0.0150 0.0050 0.111 Concentration at time 2 (mol L -1 ) 0.0100 0.0100 0.0150 2.25 Concentration at time 3 (mol L -1 ) 0.0037 0.0037 0.0276 56 The Reaction Quotient and the Equilibrium Constant Law of equilibrium: for a given reaction at a specified temperature , all equilibrium mixtures have the same alue of the reaction quotient ( This numerical value value of the reaction quotient ( Q ). This numerical value of Q is called the equilibrium constant ( K ). The Reaction Quotient and the Equilibrium Constant The form of Q and K For reactions involving solids, concentration terms for the lids are not incl ded in e pressions for K solids are not included in expressions for Q or K. CaCO 3 (s) CaO(s) + CO 2 (g) For reactions taking place in aqueous solution, the molar concentration of water is not included in expressions for Q 2 CO Q p Q or K. NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq)  3 4 NH OH NH Q The Reaction Quotient and the Equilibrium Constant Activity-based Equilibrium Constants eaction quotients are most correctly expressed as Reaction quotients are most correctly expressed as functions of activities of species rather than as concentrations. Activities are measures of effective concentration, and as a ratio compared with 1 mol L -1 , are unitless. sufficiently dilute solutions (which is concerned in In sufficiently dilute solutions (which is concerned in this text), there is negligible difference between the concentrations and activities of species.
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3 The Reaction Quotient and the Equilibrium Constant The Relationship between Q and K in Reaction ixtures Mixtures Reactants and products: the species on the left and right sides of the written reaction equation, respectively.
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15 - GENERAL CHEMISTRY Principles and Modern Applications...

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