Collision Theory
Quick Notes
- Reactions occur when particles successfully collide with:
- Sufficient energy (≥ activation energy)
- Correct orientation (collision geometry)
- The greater the frequency of successful collision, the faster the rate of reaction
- Kinetic energy of particles increases with temperature (in kelvin).
- Higher temperature means more particles have required activation energy, increasing frequency of successful collisions (faster reaction).
- Not all collisions result in a reaction — only successful collisions do.
Full Notes
Collision Theory
For a chemical reaction to occur reactant particles must collide and the collisions must occur with:
- Enough energy to overcome the activation energy barrier.
- Proper alignment so bonds can break/form (correct geometry).
These are called successful collisions.
Activation Energy (Ea)
The activation energy (Ea) is the minimum energy required for a reaction to proceed.
If particles collide with less energy than the required activation energy, they bounce off each other unchanged – no reaction occurs.
The Role of Temperature
Temperature is a measure of the average kinetic energy of particles.
As temperature increases, particles move faster and collide more often. More particles have enough energy to overcome Ea, so reaction rate increases.
This is why many reactions go faster when heated.
Collision Geometry
Even if particles collide with enough energy, they must also be oriented correctly.
Wrong orientation = no reaction, even with enough energy. This is why molecules with complex structures may react slowly, even with high energy collisions.
Example Collision Orientation
A nucleophile must approach the right part of a molecule in order for a reaction to occur.
Connection to Kinetic Molecular Theory
Kinetic molecular theory explains the movement and energy of particles in different states.
It supports collision theory by describing how increased temperature:
- Raises kinetic energy
- Increases collision frequency
- Increases fraction of successful collisions
Summary
- Collision theory explains the conditions for a successful reaction.
- Higher temperatures increase both collision energy and frequency.
- Correct collision geometry is essential for bond breaking and forming.
What is the relationship between the kinetic molecular theory and collision theory?
Kinetic molecular theory says that particles are always moving. Collision theory explains that reactions happen when these moving particles hit each other with enough energy and the right direction. So, particle motion (kinetic theory) helps us understand how collisions lead to reactions.