Collision Theory and Reaction Rate

Notes

Rates of Chemical Reactions

• The amount of time it takes for a chemical reaction to come to completion is called the reaction rate

• Reaction rates are different for different reactions– They can range from a fraction of a second to

days or even years

Why do different reactions have different rates?

• The rates of reaction are related to the properties of particles through a model called collision theory

• Particles will only react if there is an effective or successful collision between them

In order for particles to react,

1. They must collide

2. They must collide in the correct orientation to form the activated complex

• The activated complex is a temporary, unstable arrangement of atoms that may lead to products– It can be thought of as a transition state

between reactants and products

3. They must collide with a specific minimum amount of energy (activation energy) to form the activated complex

Collision theory and rate of reaction

• The rate of a reaction can be increased by changing certain factors in a reaction like temperature or concentration of reactants

• These factors will increase the reaction rate if they produce a greater number of effective collisions

• A greater number of effective collisions can be achieved by anything that– Increases the energy of the reactants – Lowers the activation energy– Produces more collisions per unit of time