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Properties of catalyst:

i. Catalysts only change the rate of a chemical reaction but itself remain unchanged in composition and amount.

ii. Catalysts are sufficient in small amounts only.

iii. For a specific reaction there is a specific catalyst and a single catalyst cannot catalyse all the reaction.

iv. Catalysts does not initiate a chemical reaction but only increases the rate of the reaction,

v. In reversible reactions catalysts equally increases the rate of forward and backward reaction.

vi. Catalysts are more efficient and effective at a particular temperature. By changing the temperature we can control their activity.

The types of catalysts are as follows –

i. Based on their physical state:

a. Heterogeneous catalyst :

When in a reaction the catalysts, reactants and products are in different physical states then the catalyst is known as heterogeneous catalyst.

Example-

Vegetable oil (l) + H₂ (g) Vegetable ghee (l)

b. Homogeneous catalyst:

When in a reaction the catalysts, reactants and products are in the same phase then the catalyst is known as homogeneous catalyst.

Example:-

2SO₂ (g)+ O₂(g) 2SO₃(g)

ii. Based on their action:

a. Positive catalyst:

The catalysts which increases the rate of a reaction are termed as positive catalyst.

Example:

2KClO₃ 2KCl + 3O₂

b. Negative catalyst:

The catalysts which decreases the rate of a reaction are termed as a negative catalyst.

Example:

2H₂O₂ 2H₂O + O₂

c. Auto-catalyst;

When the product formed in a reaction itself behaves as a catalyst, then it is known as auto-catalyst.

Example:

CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅0H

d. Bio-catalyst:

The catalyst which increases the rate of the biochemical reactions occurring in a living organism is termed as bio-catalyst. These are also known as enzymes.

Example:

Maltose Glucose