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

General Chemistry, 5th 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 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

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

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 • Kc 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 = (ngas prod) – (ngas react) Created by Tara L. Moore, MGCCC

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

Kc = ? Kc = Kp (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

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

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

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

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

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

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