Collision Theory
Collision theory is a theory regarding chemistry that makes the following assertions:
- For particles to react they must collide.
- For particles to react they must collide with sufficient energy. "Sufficient energy" is defined as the activation energy, .
- For particles to react they must collide with a certain orientation.
Something to note is that temperature is proportional to mean kinetic energy, .
Rate of Reaction
Using collision theory we can deduce the effect of different factors on the rate of reaction. (The "Effect" is increase if the reaction rate increases with an increase in the factor.)
| Factor | Effect | Explanation |
|---|---|---|
| Temperature | Increase | When the temperature is increased, the mean kinetic energy of particles increase. Since the particles have a higher velocity, they collide more frequently and there is a higher proportion of collisions with sufficient energy to react. Therefore the number of reactions per unit time increases and the reaction rate increases. |
| Addition of Catalyst | Increase | A catalyst works by adhering a number of molecules to a surface, increasing the likelihood that a collision will have the correct orientation. Essentially, it provides an alternate reaction pathway with a lower activation energy, meaning that more collisions will be successful and the rate of reaction will be higher. |
| Surface Area | Increase | The higher the surface area, the higher the number of molecules exposed to reaction. Since the number of exposed molecules is higher, the probability of collision between two molecules increases, increasing the frequency of reactions and therefore increasing rate of reaction. |
| Concentration | Increase | The higher the concentration, the higher the probability that a collision will be between two reactants, as there are fewer other particles to interfere with the reaction. Therefore, the frequency of collisions between two reactants increases, increasing the rate of reaction. |
| Pressure | Increase | The higher the pressure, the more collisions per unit time there will be, and therefore the rate of reaction will increase. |
| Volume | Decrease | The higher the volume, the further apart particles will be, decreasing the frequency of collisions and therefore the rate of reaction. |