Equilibrium 2 ppt

Chemical

Equilibrium

Chemical Equilibrium

Chemical equilibrium occurs in

chemical reactions that are

reversible. In a reaction such as:

CH

(g) + H

O(g)



CO(g) + 3H

(g)

The reaction can proceed in both

directions

An Equilibrium System

CH

(g) + H

O(g)



CO(g) + 3H

(g)

 After some of the products are created the products begin to react to form the reactants

 At equilibrium there is no net change in the concentrations of the reactants and products

 The concentrations do not change but

Chemical Equilibrium

 _CH

4(g) + H2O(g) <=> CO(g) + 3H2 (g)



At the beginning of the reaction, the

rate that the forward direction is

higher



As the reactants decrease the rate in

the forward direction slows



As the products form, the rate in the

reverse direction increases



When the two rates are the same

Dynamic Equilibrium

An equilibrium is Dynamic

CH

(g) + H

O(g)



CO(g) + 3H

(g)

The amount of products and the

reactants are constant.

The Equilibrium Constant

aA + bB



cC + dD

The upper case letters are the molar

concentrations of the reactants and

products. The lower case letters

The Equilibrium Constant

Equilibrium Constant

Calculations

Example

N

(g) + 3H

(g)



2NH

(g)

At equilibrium, a one-liter container has

1.60 moles NH

, .800 moles N

, and

1.20 moles of H

. What is the

Equilibrium Constant

Calculations

At equilibrium, a one-liter container has

1.60 moles NH

, .800 moles N

, and 1.20

moles of H

. What is the equilibrium

Reaction quotient



The equilibrium constant is a constant

ratio only when the system is in

equilibrium.



If the system it not at equilibrium the

ratio is known as a Reaction Quotient



If the reaction quotient is equal to the

Using Equilibrium Constants

for other calculations

If a solution is not at equilibrium the ratio of the right side over the left is called a reaction

quotient

.

Equilibrium Constants and

calculations

If Q > Keq , the product side is too high and the equilibrium will shift to the left to restore

equilibrium

Equilibrium Calculations –

Using I. C. E. Models

Equilibrium constants and

concentrations can often be

deduced by carefully examining

data about initial and equilibrium

concentrations

Equilibrium Calculations

ICE Model problem 1

H₂ + I₂  2HI

Suppose that 1.5 mole of H2 and 1.2 mole of I2 are placed in a 1.0 dm3 container. At equilibrium it was

Equilibrium Calculations

ICE Model Problem 1 Solution

H₂ + I₂  2HI

Suppose that 1.5 mole of H2 and 1.2 mole of I2 are placed in a 1.0 dm3 container. At equilibrium it was found that there were 0.4

mole of HI. Calculate the equilibrium concentrations of [H₂] and [I₂] and the equilibrium constant.

I C E Since 2x = 0.4, x = 0.2

[H₂ ] 1.5 -x 1.5- x [H₂ ] = 1.5 – 0.2 = 1.3

[ I₂ ] 1.2 -x 1.2 –x [I₂ ] = 1.2 – 0.2 = 1.0

[HI ] 0 +2x 0.4

Keq = [HI]2 . _{= (0.4)}2 _{= 0.123}

Equilibrium Calculations

ICE Model Problem 2

2 SO₂ + O₂  2SO₃

Suppose that 1.4 mole of SO2 and 0.8 mole of SO3 are placed in a 1.0 dm3 container. At equilibrium it was

found that there were 0.6 dm3 of SO

3. Calculate the

Equilibrium Calculations

ICE Model Problem 2 Solution

2 SO₂ + O₂  2SO₃

Suppose that 1.4 mole of SO2 and 0.8 mole of SO3 are placed in a 1.0 dm3 container. At equilibrium it was found that there were 0.6

dm3 of SO

3. Calculate the equilibrium concentrations of [SO2]

and [O₂] and the equilibrium constant.

I C E Since 2x = 0.6, x = 0.3

[SO₂ ] 1.4 -2x 1.4-2x [SO₂ ] =1.4 – 2( 0.3) = 0.8

[O₂ ] 0.8 -x 0.8 –x [O₂ ] = 0.8 – 0.3 = 0.5

[SO₃] 0 +2x 0.6

Keq = [SO₃]2 . = (0.6)2 = 0.281

[SO₂ ]2 _[O

Le Chatelier’s Principle



Le Chatelier's Principle

states: When a

system in chemical equilibrium is disturbed

by a change of temperature, pressure, or a

concentration, the system shifts in

equilibrium composition in a way that tends

to counteract this change of variable.



A change imposed on an equilibrium

system is called a

stress



The equilibrium always responds in such a

Le Chatelier’s Principle



Types of stresses



Change in concentration of one or

more reactants or products



Change in temperature



Change in pressure

Effect of a Change in

Temperature



An increase in the temperature causes the

equilibrium to shift in the direction of the

endothermic reaction



N

2

(g) + 3 H

(g)



2NH

(g)



Since



H is negative the endothermic

reaction is the reverse direction. An

increase in temperature causes the reaction

to shift to the left, resulting in an increase in

Effect of a Change in

Pressure

 Pressure affects only gases in an equilibrium

 PV = nRT

 An increase in pressure causes the equilibrium to

shift in the direction that has the fewer number of moles



N

(g) + 3 H

(g)



2NH

(g)

 An increase in pressure results in a an decrease in

Effect of a Change in one of

the reactants or products



The equilibrium responds in such a way so

as to diminish the increase



Substances on the same side of the arrow

respond in opposite directions.



Substances on the opposite side of the

arrow move in the same direction



N

2

(g) + 3 H

(g)



2NH

(g)



An increase in [N

2

] results in a decrease in

Effect of a Catalyst



Catalysts affect both the forward and

reverse directions equally



A catalyst does not change the