# Factors Affecting Rate of Reaction - Explanation by Collision Theory

#### Total Surface Area of Reactants

1. When the size of the solid substance that reacts is smaller, its total surface area exposed becomes larger.
2. This causes the collisions frequency between the reactants increases.
3. As a result, the frequency of effective collisions also increases and hence increases the rate of reaction.

#### Concentration

1. Solution with higher concentration has more particles per unit volume in the solution.
2. As a result, the collisions frequency between the reactants increases.
3. Consequently, the frequency of effective collisions also increases and hence the rate of reaction increases.

#### Temperature

1. When the temperature of a reaction increases, the particles of the reacting substances move faster.
2. This causes the collisions frequency between the reactants increases.
3. As a result, the frequency of effective collisions also increases and hence increases the rate of reaction.

#### Presence of Catalyst

1. When a positive catalyst is used in a reaction, the catalyst prepares an alternative path with lower activation energy for the reaction.
2. As a result, the frequency of effective collisions increases and hence increases the rate of reaction.

#### Pressure of Gas

1. For a reaction that involves a gas, when pressure increases, the particles of gas are compressed to fill the spaces which are small. This makes the number of particles of gas per unit of volume to increase.
2. This causes the collisions frequency between the reactants increases.
3. As a result, the frequency of effective collisions also increases and hence increases the rate of reaction.