Monday, 19 January 2015

1.3 Collision Theory

The collision theory
■ Collision theory

A chemical reaction may occur as a result of the collisions between particles.

For a reaction to occur, an effective collision must take place.
■ Effective collision

The particles of the reactants must collide with each other to produce energy that greater than or equal to the activation energy.

The collisions must happen in the correct orientation.

The animation below shows the collisions of particles.
■ This video contains information on the collision theory in the rate of reaction.

■ Activation energy (Ea)

Minimum amount of energy required to initiate a chemical reaction.

Energy profile diagram can be used to shows the energy change that takes place in a chemical reaction.
Energy profile diagram for exothermic reaction
Energy profile diagram for endothermic reaction

This video contains information on the effective collision and activation energy.

Example: Reaction of hydrogen with iodine to produce hydrogen iodide.
H2(g) + I2(g) → 2HI(g)
■ Use of collisions theory to explain the rate of reaction:

Relationship of frequency of effective collisions and rate of reaction
Reaction with higher frequency of effective collisions means the rate of reaction is higher.

Relationship of activation energy and rate of reaction
Reaction with high activation energy occurs slowly while the reaction with a low activation energy occur quickly.


Collision theory and the effect of surface area (particle size)
■ The effect of the size of reactant

If the size of the solid material that reacts is small, the amount of surface area exposed to reaction increased.

The chance for collisions increased, the collision frequency is also increased, resulting in the increased of effective collisions.

The rate of reaction also increased.

The animation below shows the effect of size of reactant on the rate of reaction.


Collision theory and the effect of concentration
■ The effect of concentration

When the concentration increases, the number of particles per unit volume increases.

Therefore, the total number of collisions and the effective collision frequency between particles of materials response will increase.

Thus, the reaction rate increases.

The animation below shows the effect of concentration on the rate of reaction.


Collision theory and the effect of temperature
■ The effect of temperature

When the reaction temperature increased, the particles of the reactants have more kinetic energy.

Particles reactants move more quickly.

This increases the chances of a collision, the collision frequency is increased.

Then the effective collision frequency increases and the rate of reaction increases.

The animation below shows the effect of temperature on the rate of reaction.


Collision theory and the effect of catalyst
■ The effect of catalyst

Catalysts change the rate of a reaction by varying the activation energy of the reaction.
■ Positive catalysts

Provide a reaction path requires a lower activation energy.

More particles will have enough energy to overcome the lower activation energy.

The effective collision frequency is increased.

Thus, it accelerate the rate of a reaction.
■ Negative catalyst

Delay the rate of reaction by increasing the activation energy of the reaction so that the effective collision frequency is reduced.


Pressure and rate of reaction
■ The effect of pressure

When pressure increase, the particles are close together.

The number of particles per unit volume increases.

Frequency of collisions between particles increase, higher frequency of effective collisions.

More particles have activation energy, thus the rate of reaction increase.

The animation below shows the effect of pressure on the rate of reaction.



⇲ For exercise(objective and subjective), download for free on Android OS.

No comments:

Post a Comment