Chemical Equilibrium

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LEARNING OUTCOME

CHAPTER 6:

CHEMICAL EQUILIBRIUM

BY:

 Kc and Kp

 Equilibrium expressions

 Factors affecting Kc and Kp

 Conversion of Kc and Kp

 Homogeneous vs heterogeneous equilibrium

DR. LIM YING CHIN

 Le Chatelier’s Principle and the effect of temperature,

pressure, concentration and catalyst on equilibirum

WHAT IS EQUILIBRIUM?

Physical equilibrium

Equilibrium is a state in which there are no

observable changes as time goes by.

Equilibrium between 2 phases

of the same substance

Chemical equilibrium is achieved when:

• the rates of the forward and reverse reactions are

equal and

• the concentrations of the reactants and products

remain constant

rate forward = rate reverse

Example :

Vaporization of water in a

closed container

Liquid water in equilibrium

with its vapors in a closed

system at room temperature

H2O (l)

H2O (g)

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• But many other changes are reversible or do not

•

Most chemical reactions go to completion.

proceed to completion.

Example : H2(g) + I2(g)

•

2HI(g)

Some changes go only one direction

• The sign

go to completion

Example: baking bread

Flour + baking powder + water

indicates that the reaction does not

bread

• A reversible reaction is one that goes in both

directions at the same temperature.

Example:

A+B

C+D

• When there is no further change in the amounts of

reactants and products – equilibrium.

• The rates of the forward and reverse reaction are

equal - dynamic equilibrium.

rate fwd = rate rev

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Example:

A+B

C+D

Example:

A+B

C+D

• At the beginning, concentration of A & B at max.

• The rate of the reaction was at its fastest.

• As A and B react, their concentrations fall.

• They are less collide and react, the rate of

forward reaction falls as time goes on.

 With time, the rate of the reaction between C &

D increases.

 The rates of the two reactions...