Download Kinetics and Equilibrium

Chemical Kinetics
Kinetics
 Kinetics
deals with rates of
reactions (how quickly a
reaction occurs).
Kinetics: The Collision Theory
Frequency of collisions: more
collisions = faster rate
 Effective collisions: must have
1) proper orientation and
2) enough energy

Factors Affecting Rate
1. Type of substance:
 Ionic substances react faster: bonds
require less energy to break
AgNO3 (aq)+NaCl(aq)AgCl(s)+NaNO3 (aq)
In solution ionic solids dissociate into ions:
Ag+ NO3Na+
Cl-
Factors Affecting Rate

Covalent react more slowly: bonds require
more energy to break
H2 (g)+I2 (g)2 HI (g)
Bonds must be broken then be reformed.
(takes more time)
Factors Affecting Rate
2. Temperature increase
 Average kinetic energy increases and the
number of collisions increases. Reactants
have more energy when colliding. This
increases rate.
Factors Affecting Rate
3. Concentration increase
 Increases rate due to the fact that more
particles are in a given volume, which
creates more collisions.
Factors Affecting Rate
4. Surface Area Increase
 Increases rate due to increased reactant
interaction or collisions (powder vs. lump)
Factors Affecting Rate
5. Pressure Increases
 Increases the rate of reactions involving
gases only
As pressure , volume  so:
spaces between molecules 
 frequency of effective collisions
Factors Affecting Rate
6. Catalyst: substance that increases rate of
reaction, provides a shorter or alternate
pathway by lowering the activation energy
of the reaction.
 Catalysts remain unchanged during the
reaction and can be reused.

Activation energy: amount of energy
required to “start” a reaction
Quick Review –
Factors that affect reactions

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Ionic solutions have faster reactions than
molecule compounds. (bonding)
Temp.  Rate
 conc. rate
 surface area  rate
 Pressure  rate,  P  rate
Catalysts speed up reactions.
Potential Energy Diagrams

A potential energy diagrams graphs heat
during the course of a reaction.
Potential Energy Diagrams

In an endothermic process, the potential
energy (PE) of products is more because
energy is gained.
Potential Energy Diagrams

In an exothermic process, the potential
energy (PE) of products is less because
energy is lost.
Potential Energy Diagrams

Activation energy (Ea) is the energy level
that the reactant molecules must
overcome before a reaction can occur.
Potential Energy Diagrams

Activation energy (Ea) can be lowered by
adding a catalyst.
Potential Energy Diagrams

The activated complex is the structure at
the maximum energy point along the
reaction path. It is very unstable.
Potential Energy Diagrams

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The change in enthalpy (ΔH) is the heat
lost or gained in a chemical reaction.
ΔH = Hproducts – Hreactants
ΔH = Hproducts – Hreactants
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ΔH is positive when the reaction is
endothermic. Heat of products are greater
than reactants.
ΔH is negative when the reaction is
exothermic. Heat of reactants were
greater than the products.
Stability of Products and H
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Products tend toward lower energy
(-ΔH)
Products tend toward more randomness
(entropy)
Products of exothermic reactions are
usually more stable. Result in lower
amounts of heat.
The more negative the H, the more
stable the product is.