Created by Tara L. Moore, MGCCC

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

DefinitionsLeft 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