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

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

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

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

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

Created by Tara L. Moore, MGCCC VAN’T HOFF EQUATION The relationship between  H 0 for a reaction and its equilibrium constants at two different temperatures ln [K T2 /K T1 ] = (  H 0 /R)(1/T 1 – 1/T 2 ) Or log [K T2 /K T1 ] = (  H 0 /2.303R) (1/T 1 – 1/T 2 )

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

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

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

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

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

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

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

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

Created by Tara L. Moore, MGCCC K p = ? K p = K c (RT)  n

Created by Tara L. Moore, MGCCC K c = ? K c = K p (RT) -  n

Created by Tara L. Moore, MGCCC 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  G 0 = ?  G 0 = -RT ln K Or  G 0 = RT log K R = J/(mol*K)

Created by Tara L. Moore, MGCCC For equilibria that involve only gases The thermodynamic equilibrium constant (related to  G 0 ) is K p For those that involve species in solution, it is equal to K c

Created by Tara L. Moore, MGCCC  G 0 1 Products favored over reactants at equilibrium

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

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