11. kinetics and equilibrium

Collision Theory
In order for a reaction to
occur, the particles of the
reactant must have
enough energy, and must
collide at the correct
angles (proper
The collision theory
explains the factors that
affect the rate of a
The greater the rate of
effective collisions, the
greater the reaction rate is
The collision theory
explains the factors that
affect the rate of reaction
Factors that Affect the Rate of a
Chemical Reaction
The following factors can increase the rate of a
chemical reaction by increasing the number of
effective collisions that a occur at a given time
 Temperature
 Surface Area
 Nature of Reactants
 Catalyst
Heat of Reaction (Enthalpy)
The amount of heat given off or absorbed in a
chemical reaction. Heat of reaction is the difference
in heat content of the products and reactants. Table
I lists common reactions, and there heat of reactions.
∆H = Hproducts - Hreactants
∆H = heat of reaction
Hproducts = potential energy of the product(s)
Hreactants = potential energy of the reactant(s)
∆H is measured in kJ (kilojoules)
Table I
Remember that a -∆H
does not mean negative
energy – it only implies
an exothermic reaction
has occurred.
Potential Energy Diagrams
When the forward and reverse reactions occur
at the same rate.
The rates are equal, but the quantities
(amounts) of reactants and products are not
necessarily equal.
Types of Equilibrium:
 Phase (Dynamic)
 Solution
 Chemical
Spontaneous Reactions
A reaction that takes place under a specific set of
conditions spontaneously.
Occur in the direction of:
Less energy (lower enthalpy): favors
exothermic reactions.
 Greater entropy (disorder):
• Solids have the least entropy (most order), liquids
have more, and gases have the most entropy
• When a solid dissolves in water (salts or sugars),
entropy increases.
• At low temperature, energy is important; at high
energy, entropy is important.
Reactions Going to Completion
Some reactions go to completion; the reaction
goes in only one direction, the reactants form
products, products DO NOT form reactants.
Some indicators that a reaction has gone to
completion when the following are produced:
(1) a gas
(2) an essentially unionized product (like water)
(3) a precipitate is one of the products.
Remember that precipitates are insoluble - Table F
Le Chatelier’s Principle
Henry Louis Le Chatelier was a
French chemist who devised a
principle to predict the effect of
change in conditions on a
chemical equilibrium reaction
The principle states that if a
system at equilibrium is subjected
to stress, the equilibrium will shift
in the direction that relieves the
Types of stresses include:
concentration, temperature, and
CIA (concentration increase away)
TIA (temperature increase away)
PILM (pressure increase less moles
of gas)
CaCO3(s) + heat ↔ CaO(s) + CO2(g)
2SO3(g) + heat ↔ 2SO2(g) + O2(g)
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