Equilibrium notes .pptx

Equilibrium

2

Reversible Reactions

The conversion of reactants into products

and the conversion of products into

reactants occuring at the same time.

A + B C

3

When the forward and reverse reactions

are occurring at the same rate(speed) the

reaction is said to be in a state of

chemical equilibrium

The equilibrium position can be shown

by the double arrows and a 3

arrow

A B

1% 99%

A B

4

Equilibrium = A state in which

no net change takes place in a

5 In a reaction equilibrium, both the forward and reverse reactions are taking place simultaneously, at the same rate, so that no net change occurs.

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Dynamic

Equilibrium

=

An equilibrium in

which two or more

changes are taking

place in a closed

container

simultaneously,

but at the same

rate.

homogeneous equilibrium

–

an equilibrium in which all

reactants and products are the

same phase (liq, solid, vap.)

heterogeneous equilibrium

–

an equilibrium in which there

exist different phases of

products and reactants.

Four Conditions of Equilibrium

1. A reversible reaction is

required.

2. The observable properties of the

system (pH,colour,concentration,

pressure) remain constant.

3. Reaction must take place in a

closed system.

4. Equilibrium can be approached

from either direction of the

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Catalysts will have no effect on the

equilibrium because they speed up

both the forward and reverse reactions

equally.

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Equilibrium constants (Keq)

-Indicate if the reverse reaction will

favor reactants or products at equilibrium

aA + bB cC + dD

Keq = [C]

[D]

[A]

[B]

Keq > 1 more products than reactants at eq

Keq < 1 more reactants than products at eq

Keq expression

Assignment 4



I

C

E

Section 16.3 Equilibrium Calculations for Homogeneous Systems pg 656-661,665 (see Section 16.3 Summary pg 665)

 17D Equilibrium Calculations

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Henry Louis Le Chatelier

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Le Châtelier’s

Principle

If a stress is

applied to a

system at

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How can you shift a system that

is already in equilibrium?

By adding a stress on the system!!

Why would anyone want to shift a

system in equilibrium?

To make more product!!

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Concentration Change

Reactants Products

Increase [reactant] = shifts to use up the added reactants and produce more products Shifts right

Increase [product] = shifts to use up added product and produce more reactants Shifts left

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Decrease [reactant] = shifts to produce more reactants Shifts left

Decrease [product] = shifts to produce more product Shifts right

Reactants Products

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Effect of Temperature on a System

In Equilibrium

 Video

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A + B C + heat

A + B C + heat

Increase = favors the endothermic direction. The reaction shifts in the direction that uses up the added energy.

Temperature Change

Decreasing = favours the exothermic direction.

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NO

NO

23

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Increasing Pressure or Decreasing Volume

favors fewer gas molecules.

The reaction shifts to relieve the pressure.

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Decreasing Pressure or Increasing Volume

favors more gas molecules.

The reaction shifts to restore the pressure.

Adding and Inert substance

 The Effect of adding an Inert Substance

 The overall container pressure is altered,

but the partial

 pressures of all the reactants and

products remain

 unchanged and thus the reaction does not

Effect of Adding a Catalyst

 The Effect of Adding a Catalyst 

 Catalysts help reactions reach equilibrium

more quickly,

 but adding a catalyst to a reaction that’s

already at

 Example - Consider the reaction:  CO + H₂O l CO₂ + H₂ + heat

 In which direction will the equilibrium shift if:  a) CO₂ was removed.

 Shift right in order to make more CO₂.

 b) H₂O is added.

 Shift right in order to use up this additional H₂O

 c) Adding He gas.

 No change – gas is inert.

 d) Temp. is increased (reaction is exothermic) –  reaction shifts left to use up this heat.

e) volume is decreased –

Solubility

SOLUBILITY 

Reversible and irreversible reactions are often observed in solute-solvent systems. For example, one can observe the irreversible process of dissolving sugar in a cup of coffee. The sugar dissolves and the process stops. If,

however, we continue to add sugar to the solution, we will reach a point where no more sugar will dissolve. The solution is said to be saturated. The

dissolving action does not stop. Rather, a state of dynamic equilibrium is established.



 DISSOLVING 

UNDISSOLVED DISSOLVED SOLUTESOLUTE

Factors Affecting Solubility

 3 Actions Affecting Solubility:



 1. Nature of solute and solvent: “LIKE

DISSOLVES LIKE”

 Polar solutes dissolve readily in polar solvents.

 Eg. NaCl dissolves in H₂O

 Non-polar solutes dissolve in non-polar solvents.

Factors Affecting Solubility

 2. Temperature:

 For most solids dissolving in liquids, an

increase in temperature results in an

increase in solubility. Such reactions are

usually endothermic.

 For most gasses dissolving in liquids, a

decrease in temperature results in an

Factors Affecting Solubility

 3. Pressure:

 While changes in pressure do not affect

the solubility of solids or liquids, the

solubility of gasses in liquids is directly

 K_sp The Solubility Product Constant 

 An ELECTROLYTE is anything that will dissolve to form a

solution that will conduct electricity. All ionic compounds ionize in solution.

 NaCl in water ionizes to become Na+ and

Cl-

A saturated solution is in a state of dynamic equilibrium. The rates of dissolving and recrystalizing are equal and will remain constant if temperature, pressure and

Solubility Constant

 Solubility is a characteristic property of a

compound.



 Eg.

 AgBr _(s) Ag+_(aq) + Br-_(aq)

 Because AgBr is a solid, it is not included in K_sp

calculations.

