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General Chemistry, 5 th ed. Whitten, Davis & Peck

General Chemistry, 5 th ed. Whitten, Davis & Peck. Definitions Left click your mouse to continue. DIRECTIONS. This slide show presentation is designed to function like flash cards. To check your answer, and/or to move on to the next slide, simply left click your mouse.

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General Chemistry, 5 th ed. Whitten, Davis & Peck

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  1. General Chemistry, 5th ed.Whitten, Davis & Peck Definitions Left click your mouse to continue. Created by Tara L. Moore, MGCCC

  2. DIRECTIONS • This slide show presentation is designed to function like flash cards. • To check your answer, and/or to move on to the next slide, simply left click your mouse. Created by Tara L. Moore, MGCCC

  3. ACTIVITY (of a component of an ideal mixture) A dimensionless quantity whose magnitude is equal to molar concentration in an ideal solution, equal to partial pressure (in atmospheres) in an ideal gas mixture, and defined as 1 for pure solids or liquids Created by Tara L. Moore, MGCCC

  4. CHEMICAL EQUILIBRIUM A state of dynamic balance in which the rates of forward and reverse reactions are equal; there is no net change in concentrations of reactants or products while a system is at equilibrium Created by Tara L. Moore, MGCCC

  5. DYNAMIC EQUILIBRIUM An equilibrium in which processes occur continuously, with no net charge Created by Tara L. Moore, MGCCC

  6. EQUILIBRIUM CONSTANT, K • A quantity that indicates the extent to which a reversible reaction occurs • Its magnitude is equal to the mass action expression at equilibrium • K varies with temperature Created by Tara L. Moore, MGCCC

  7. HETEROGENEOUS EQUILIBRIA Equilibria involving species in more than one phase Created by Tara L. Moore, MGCCC

  8. HOMOGENEOUS EQUILIBRIA Equilibria involving only species in a single phase; all gases, all liquids, or all solids Created by Tara L. Moore, MGCCC

  9. LeCHATELIER’S PRINCIPLE If a stress (change of conditions) is applied to a system at equilibrium, the system shifts in the direction that reduces the stress Created by Tara L. Moore, MGCCC

  10. MASS ACTION EXPRESSION aA + bB  cC + dD Q (or K at equilibrium) = [C]c[D]d [A]a[B]b Created by Tara L. Moore, MGCCC

  11. REACTION QUOTIENT, Q • The mass action expression under any set of conditions (not necessarily equilibrium) • Its magnitude relative to K determines the direction in which reaction must occur to establish equilibrium Created by Tara L. Moore, MGCCC

  12. REVERSIBLE REACTIONS Reactions that do not go to completion and occur in both the forward and reverse directions Created by Tara L. Moore, MGCCC

  13. VAN’T HOFF EQUATION The relationship between H0 for a reaction and its equilibrium constants at two different temperatures ln [KT2/KT1] = (H0/R)(1/T1 – 1/T2) Or log [KT2/KT1] = (H0/2.303R) (1/T1 – 1/T2) Created by Tara L. Moore, MGCCC

  14. For any reaction, the value of Kc (equilibrium constant) • Varies only with temperature • Is constant at a given temperature • Is independent of the initial concentrations Created by Tara L. Moore, MGCCC

  15. Q < K Forward reaction predominates until equilibrium is established Created by Tara L. Moore, MGCCC

  16. Q = K System is at equilibrium Created by Tara L. Moore, MGCCC

  17. Q > K Reverse reaction predominates until equilibrium is established Created by Tara L. Moore, MGCCC

  18. If a change of conditions (stress) is applied to a system at equilibrium • The system responds in the way that best tends to reduce the stress in reaching a new state of equilibrium • Concentration changes • Pressure changes (volume for gas phase) • Temperature changes • Introduction of catalysts Created by Tara L. Moore, MGCCC

  19. When a “new equilibrium” is established • The rates of the forward and reverse reactions are equal again • Kc is again satisfied by the concentrations of reactants and products Created by Tara L. Moore, MGCCC

  20. A decrease in volume (increase in pressure) Shifts the reaction in the direction that produces the smaller number of moles of gas Created by Tara L. Moore, MGCCC

  21. An increase in volume (decrease in pressure) Shifts the reaction in the direction that produces the larger number of moles of gas Created by Tara L. Moore, MGCCC

  22. If there is no change in the number of moles of gases in a reaction A volume (pressure) change does not affect the position of equilibrium Created by Tara L. Moore, MGCCC

  23. An increase in temperature Favors endothermic reactions Created by Tara L. Moore, MGCCC

  24. A decrease in temperature Favors exothermic reactions Created by Tara L. Moore, MGCCC

  25. n = ? n = (ngas prod) – (ngas react) Created by Tara L. Moore, MGCCC

  26. Kp = ? Kp = Kc(RT) n Created by Tara L. Moore, MGCCC

  27. Kc = ? Kc = Kp (RT)- n Created by Tara L. Moore, MGCCC

  28. For pure solids or liquids The activity is taken as 1, so terms for pure liquids and pure solids do not appear in the K expression for heterogeneous equilibria Created by Tara L. Moore, MGCCC

  29. G0 = ? G0 = -RT ln K Or G0 = -2.303 RT log K R = 8.314 J/(mol*K) Created by Tara L. Moore, MGCCC

  30. For equilibria that involve only gases The thermodynamic equilibrium constant (related to G0) is Kp For those that involve species in solution, it is equal to Kc Created by Tara L. Moore, MGCCC

  31. G0 < 0; K > 1 Products favored over reactants at equilibrium Created by Tara L. Moore, MGCCC

  32. G0 = 0; K = 1 At equilibrium when [C]c[D]d…=[A]a[B]b…. (very rare Created by Tara L. Moore, MGCCC

  33. G0 > 0; K < 1 Reactants favored over products at equilibrium Created by Tara L. Moore, MGCCC

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