Collision Theory And Activation Energy
Dr. Davinder Bhachu
Teacher
Contents
Collision Theory
Key principle
For a reaction to occur, particles must:
1. Collide with each other.
2. Collide with enough energy to break old bonds and form new ones.
Why rate changes
Anything that increases:
How often particles collide, or
How energetic those collisions are, will make the reaction go faster.
Activation energy
Reactions only occur when collisions have at least a minimum amount of energy known as the activation energy.
Why temperature matters again
Increasing temperature:
Not only makes collisions more frequent,
It also makes a higher proportion of collisions have energy equal to or greater than the activation energy.
Thus, temperature has a double effect on rate.
Rate and Proportionality
The rate of a reaction is directly proportional to the number of successful collisions each second.
Example
During the reaction between sodium thiosulfate and hydrochloric acid, the time until the solution clouds over is recorded at various temperatures. If increasing the temperature from 20 °C to 30 °C cuts the reaction time in half, then the frequency of successful collisions has roughly doubled.