Chemistry Chapter 9 – Collision Theory Teacher: H. Michael Hayes

‘Learning Objectives’ You will learn the significance of molecular collisions relative to chemical reactions. Types of collisions Reaction mechanism explained by collision theory.

Types of Collisions There are two major types of collisions: Elastic Collisions: Reactant particles hit each other but no reaction results! Inelastic Collisions: Reactant particles hit each other and set off a chemical reaction that transforms reactants into products. Two conditions MUST be met for a collision to be inelastic. Reaction particles must have the ‘correct’ orientation (collision geometry) Reactant particles must have energy equal to or greater than the activation energy of the R x

Relationship between E a and collisions. The Activation Energy is the minimum collision energy required for a reaction to occur. The distribution curve shows those molecules possessing sufficient energy to react. The larger the hatched area the faster the reaction rate.

Reaction mechanism explained by collision theory The Activation Energy is the minimum collision energy required for a reaction to occur. Collision theory explains the interactions between reactant particles and the energy present at each stage in the evolution of a reaction as illustrated by the reaction mechanism. The reaction sequence is demonstrated buy and ENERGY DIAGRAM

Complex reaction using collision theory An overall reaction can consist of several intermediate steps – ELEMENTARY REACTIONS. The rate of the overall reaction is dependent on the greatest Activation Energy. In the diagram to the left it is STEP 3 that determines the overall rate of the reaction since it has the highest E a.

Collision Theory Done! – We now move on to Chapter 10 – Factors Affecting Reaction Rates.