CHEMICAL EQUILIBRIA | 4.1

Equilibrium

state in which there are no observable changes as time goes by

Chemical Equilibrium is achieved when

macroscopically, molecular level 

in the characteristic of chemical equilbrium

*****, reaction may appear to have stopped

**** ****, the forward and reverse reactions are constantly occuring 

Law of Mass Action

expresses the relative concentrations of reactants and products at

equilibrium in any reaction

Equilibrium Constant (Keq)

- temperature dependent

has no units (dimensionless)

product predominates

Keq»»»1

Reactant Predominates 

Keq«««1 

Kp Expression

Kc Expression

kp and kc law

universal gas constant (0.082056 L-atm/mol-K)

R = ****

= no. of moles of gaseous products – no. of moles of

gaseous reactants

∆n

Homogenous Equilibria

refers to reactions where all the species are in the same phase

Heterogenous Equilibria

refers to reactions where reactants and

products are of different phases

- The concentrations of pure solids, pure

liquids and solvents do not appear in

the equilibrium constant expressions.

Reaction Quotient (Q)

used to determine if the given reaction is at equilibrium, and if it

is not, the direction in which the reaction will proceed to attain

equilibrium

- same expression with the Keq

In equilibrium

Q=Keq

Reaction to Product (Shift to Right)

Q<Keq

Product to Reactant (Shift To Left)

Q>Keq

partially offset, equilibrium position

If an external stress is applied to a system at equilibrium, the

system adjusts in the direction that the stress is *****

the stress as the system reaches a new ***** *****.

consume

If a reactant or product is added, the equilibrium will shift in the

direction that will *** the added substance

replace the removed

If a reactant or product is removed, the equilibrium will shift in

the direction that will **** **** *** substance

Change in Temperature

the only factor that can change the value of the equilibrium

constant

endothermic (+)

HEAT = Reactant (in an ***** reaction)

exothermic (-)

HEAT = Product (in an ****** reaction)

Endothermic reaction: Heat = Reactant

Exothermic reaction: Heat = Product

reduces

if pressure is increased (will decrease in volume), the system will shift towards the direction which **** the total number of gaseous molecules.

increases

if pressure is decrease (will increase in volume), the system will shift towards the direction which the **** total number of gaseous molecules.

does not change K

• does not shift the position of an equilibrium system

• system will reach equilibrium sooner

Effect of Catalyst