Collision Theory Collision Theory What is necessary for

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Collision Theory

Collision Theory

Collision Theory • What is necessary for a chemical reaction to occur? • Collision

Collision Theory • What is necessary for a chemical reaction to occur? • Collision theory – theory that a reaction occurs when an effective collision occurs between reactants (atoms, molecules or ions) • What makes a collision effective?

Effective Collisions 1. the orientation of the reactants (the collision geometry) must be favourable

Effective Collisions 1. the orientation of the reactants (the collision geometry) must be favourable 2. the collision must occur with sufficient energy

Orientation

Orientation

Energy • Activation energy (Ea) – the minimum collision energy required for the reaction

Energy • Activation energy (Ea) – the minimum collision energy required for the reaction to take place • This energy is needed first to break the bonds in the reactants and then to form new bonds in the products

Energy Diagram • energy diagrams show change in energy during a reaction Ea ΔH

Energy Diagram • energy diagrams show change in energy during a reaction Ea ΔH

Activated Complex • activated complex – a chemical species temporarily formed by the colliding

Activated Complex • activated complex – a chemical species temporarily formed by the colliding reactant molecules before the final product of the reaction is formed

Activated Complex • transition state – the highest energy state between reactants and products

Activated Complex • transition state – the highest energy state between reactants and products during which bonds are being broken and formed.

Ea • How will activation energy affect the rate of a reaction? • The

Ea • How will activation energy affect the rate of a reaction? • The higher the activation energy the fewer the effective collisions and the slower the reaction

Exothermic and Endothermic Reactions ΔH ΔH • Enthalpy ( H) – measure of heat

Exothermic and Endothermic Reactions ΔH ΔH • Enthalpy ( H) – measure of heat absorbed or released • H = Hproducts - Hreactants • Exothermic – energy of products is less than reactants ( H negative) • Endothermic – energy of products is greater than reactants ( H positive)

Factors Affecting Reaction Rate 1. 2. 3. 4. 5. Nature of reactants Temperature Concentration

Factors Affecting Reaction Rate 1. 2. 3. 4. 5. Nature of reactants Temperature Concentration Surface Area Catalysts

Nature of Reactants • e. g. Bond strength • e. g. state, gases have

Nature of Reactants • e. g. Bond strength • e. g. state, gases have more collisions

Temperature • higher temperature more kinetic energy more collisions

Temperature • higher temperature more kinetic energy more collisions

Concentration • more particles more collisions

Concentration • more particles more collisions

Surface Area • more exposure to collisions, faster reaction – lump reacts more slowly

Surface Area • more exposure to collisions, faster reaction – lump reacts more slowly

Catalysts • Catalyst – substance that increases the rate of a reaction without being

Catalysts • Catalyst – substance that increases the rate of a reaction without being consumed • It works by lowering activation energy

Inhibitor • inhibitor – slows a reaction

Inhibitor • inhibitor – slows a reaction

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