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Catalyst: A substance that can influence the rate of a chemical reaction but itself does not undergo the permanent chemical change.

Catalyst increases the reaction rate by lowering the activation energy of the reactant.

Catalyst increases the reaction rate by lowering the activation energy of the reactant.

Eq → Activation energy without catalyst
Eq → Activation energy with catalyst
ER → Energy of reaction
A → Path of reaction without catalyst
B → Path of reaction with catalyst.

Catalysis: The process in which rate of reaction is influenced by catalyst is called catalysis.

Substrate: The reactant on which catalyst acts is called substrate.

Catalyst does not change the heat of reaction it only makes a process faster.

Catalyst does not change the yield of the product

Type of Catalyst:

Positive Catalyst: A catalyst which increase the rate of reaction by lowering the activation energy of reaction.

Positive Catalyst

Example :

Positive Catalyst

Negative Catalyst: A catalyst that retards the chemical reaction by raising the energy barrier or activation energy.

Negative Catalyst

Example:

Negative Catalyst

Types of catalysis

Homogeneous Catalysis: Catalysis in which catalyst and reactants are present in same phase.

Example:

Homogeneous Catalysis

Heterogeneous Catalysis:  Catalysis in which Catalyst and reactants are in different phase.

Example:

Homogeneous Catalysis

Effect of catalyst on the Rate of Reaction:

According to the Arrhenius theory

Effect of catalyst on the Rate of Reaction

Thus specific rate of reaction (rate constant k) depends upon two factors

  1. Ea
  2. T

when we employ catalyst Ea of reaction is lowered and more no. of molecules possesses energy above the threshold temperature rate of reaction increases.

If at temperature T rate constant is K1 for uncatalyzed reaction and rate case is K2 for catalyzed reaction

Effect of catalyst on the Rate of Reaction

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Class 12 Chemistry Chemical Kinetics All Topics Notes CBSE Class 12 Chemistry All Chapters Notes

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