What is catalyst in chemistry Class 10?

We will discuss the definition of catalyst, types of catalysts, and examples of catalysts in this article.

1.  Definition of catalyst

2.  Types of catalysts with examples

3.  Properties of catalyst

4.  Factors affecting the action of catalysts

1.  Definition of catalyst

 Those substances which change the velocity or speed of a chemical reaction but remain unchanged during the reaction are called catalysts. This phenomenon is known as catalysis.

    

2.  Types of catalysts with examples

Catalysts can be classified on the basis of the following factors

i.              On the basis of the physical state

ii.           On the basis of action

i.              On the basis of physical state: - catalysts are of two types on the basis of physical state

a.   Homogenous catalysts

b.  Heterogenous catalysts

    

    a.   Homogenous catalyst: - When catalyst, reactants, and products are in the same physical state in a chemical reaction, then the catalyst is known as homogenous catalyst and the reaction is known as homogenous catalysis.

    `CH_3COOCH_{3(l)} +H_2O_{(l)} \overset{HCl_(aq)}{\rightarrow}CH_3COOH_{(aq)}+CH_3OH_{(aq)}`

    

   In the reaction reactants, catalysts and products are in a liquid(aqueous) state.

   b.  Heterogenous catalyst: - When catalyst, reactants, and products are in different physical states then the catalyst is called a heterogenous catalyst and the reaction is known as heterogenous catalysis.  

        `N_{2(g)} + 3H_2(g) \overset{Fe(s)}{\rightarrow}2NH_{3(g)}`

    

   ii.           On the basis of action: - Catalysts are of the following types on the basis of their action

   

   a.    Positive catalyst

   b.  Negative catalyst

   c.   Auto catalyst 

   d.  Bio catalyst

a.   Positive catalyst: - Catalysts that increase the rate of chemical reactions are called positive catalysts.

 `2KClO_3\overset{MnO_2}{\rightarrow}2KCl + 3O_2`

  `2SO_2 + O_2\overset{V_2O_5}{\rightarrow}2SO_3`

`MnO_2` and `V_2O_5` increase the rate of reaction so they are positive catalysts.

b.  Negative catalyst: - Catalysts that decrease the rate of a chemical reaction is called negative catalysts.

 `2H_2O \overset{glycol}{\rightarrow} 2H_2O + O_2`

`2CHCl_3\overset{C_2H_5OH}{\rightarrow}2COCl_2 + 2HCl`

Glycol and ethanol decrease the rate of reaction, so they are negative catalysts.

c.   Auto catalyst: - When the product formed in a chemical reaction itself acts as a catalyst and increases the speed of the chemical reaction is called an auto catalyst.

`CH_3COOC_2H_5 + H_2O→ CH_3COOH+ C_2H_5OH`

The reaction is slow in the beginning but when some amount of acetic acid (`CH_3COOH`)is formed, the rate of reaction increases, and acetic acid acts as an auto catalyst.

d.  Bio catalyst: - The substance which is used to increase the speed of biochemical reactions is called a biocatalyst. Enzymes are biocatalysts.

Enzymes are complex nitrogenous organic compounds and are specific for particular biochemical reactions.

    `NH_2CONH_2+ H_2O \rightarrow \overset{urease}{\rightarrow}2NH_3 + CO_2`

   Urease is an enzyme that acts as a biocatalyst.

3.  Properties of catalyst

i.               Catalysts only change the rate of reaction.

ii.           Catalysts do not take part in the reaction and remain unchanged during the reaction.

iii.        Small amount of catalyst is sufficient.

iv.         A single catalyst does not catalyze all the chemical reactions in the same manner.

v.            Catalysts do not initiate or start a chemical reaction.

vi.         In reversible reactions, catalysts affect the rate of both forward and backward reactions in the same manner.

 

 

4.  Factors affecting catalysts

The activity of catalyst can be affected by the following factors

i.              Catalyst promotor

ii.           Catalyst inhibitor

iii.        Temperature

i.              Catalyst promotor: - Those substances which when added to a catalyst in a chemical reaction increase the activity of the catalyst are called catalyst promotors. These substances only increase the activity of the catalyst.

     `2N_2  + 3H_2 \overset{Fe(Mo)}{\rightarrow}2NH_3`

    Fe acts as a catalyst in the reaction and molybdenum acts as a catalyst promotor.

    `\text{Vegetable oil} + H_2 \overset{Ni(Cu)}{\rightarrow} \text{vegetable ghee}`

Ni acts as a catalyst and Cu is a catalyst promotor.

ii.           Catalyst inhibitor: -  Those substances which when added to a catalyst in a chemical reaction decrease the activity of the catalyst are called catalyst inhibitors.

    `N_2+ 3H_2 \overset{Fe(CO)}{\rightarrow} 2NH_3`

 

 

Iron acts as a catalyst and carbon monoxide acts as a catalyst inhibitor.

iii.   Change in temperature also affect the activity of catalysts.

 

Related Topics

1. What happens during a chemical reaction

 FAQs

1. Define catalyst.

Ans.  A catalyst is a substance that changes the rate of a chemical reaction.

2. How can the activity of catalysts be affected?

Ans. The activity of catalysts can be affected by catalyst promotor, catalyst inhibitor, and temperature.

3. How do catalysts work?

Ans. The catalyst appears in the complete mechanism of a chemical reaction but does not appear in the reactant side and product side.it only changes the speed of the reaction.