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Chemical Catalyst

Chemical Catalyst in Chemistry

Chemical catalyst is defined as a substance which affect to enhance the speed of reaction rate itself without effect on its activity, mass, and chemical composition. Hence the catalytic activity of catalysts action on the kinetics rate of the reaction by changing activation or free energy without effect on the equilibrium. For example, the ionic hydrogen uses as a catalyst in the acid catalysis reaction of sugar or ester in chemistry. Hence the chemical catalyst provides the alternate path of lower activation energy to the reaction. Therefore, decreases in activation energy result in an increase in reaction rate is called catalysis. When the substances slow down the rate of the chemical reactions are called negative catalysts. These substances also called inhibitors. For example, sulfuric acid acts as an inhibitor in the decomposition of hydrogen peroxide.

Catalytic Activity and Activation Energy

The catalytic reaction occurs when the activity of substance increase by lowering the activation energy of the catalyst in chemistry.

Activation energy and effect of catalyst in equilibrium reaction in chemistry


For homogeneous catalysis, catalyst provides an alternative path in which the activation energy lowered. Lesser unit of activation energy permits a larger amount of reactants to react in a given time. For example, uncatalyzed decomposition of ethyl either found to be a unimolecular reaction with activation energy 53 kcal/mol. When iodine vapor used, the reaction becomes bimolecular with activation energy 35 kcal/mol.

Effect of Catalyst on the Rate of Reaction

The catalyst remains unchanged in the mass, density, concentration, and composition of constitute atoms at the end of the reaction. However, the physical state like particle size or color of the catalyst maybe alter. For example, manganese dioxide used in the decomposition of potassium chlorate becomes finely divided powder after the reaction.

A catalyst can effect the rate of chemical reactions but can not start a reaction. Therefore, it only increases the speed of the chemical reaction. A catalyst itself not consumed during the course of the reaction and regenerate at the end of the reaction. For example, 1.7 gm Platinium produces 1.8 cc of oxygen per minute from the decomposition of hydrogen peroxide. Platinium elements remain active even production of 10 lit of oxygen.

How do Catalysts Effect Equilibrium?

The catalysts do not Effect the final state of equilibrium. The Van’t Hoff reaction isotherm, ΔG0 = – RT lnk, where k = equilibrium constant Since the catalyst does not contribute any energy to the system to increases the free energy but increases the entropy of the system. Hence thermodynamics free energy remains the constants as the presence or absence of the catalyst. Thus k also remains the same and the position of equilibrium remains unaltered. But equilibrium constant k = k1/k2, where k1 and k2 = rate of forward and backward reaction.

Therefore, when the catalyst increases the rate of the forward process, k1 increases. Hence, in order to keep k constant, k2 also increases to the same extent. The catalysts thus affect to enhancing the rate of both forward and backward reaction, helps to attain equilibrium more quickly. But it does not affect the equilibrium according to the Le Chatelier principle.

Catalytic Action of Catalyst

The catalytic action of catalyst is specific, thus it can not be used for every reaction. For example, manganese dioxide can catalyze the decomposition of potassium chlorate but not potassium nitrate. However, the change of catalyst changes the nature of the product of the reaction. For example, carbon monoxide and hydrogen in the presence of nickel produce methane but in the presence of zinc oxide produce methyl alcohol.

CO + H2 → CH4 + H2O (presence of Ni)
CO + H2 → CH3OH (presence of ZnO)

HCOOH → H2 + CO2 (presence of Cu or ZnO)
HCOOH → H2O + CO (presence of Al2O3)

An optimum temperature at which the efficiency of a catalyst is most marked. In Learning chemistry, the catalytic action of enzyme increase with the rise of specific heat but the efficiency falls down after a certain temperature due to the coagulation of the enzyme.

Catalyst Used in Chemical Reaction

List of catalyst chemistry example used for the chemical reaction are two main types

  1. Homogeneous catalysis: The catalyst present in the same phase (solid, liquid, or gas phase) as the reacting substances.
  2. Heterogeneous catalysis: The catalyst is present in a different phase from the reactant.
  • The catalyzed reaction for the dissociation of potassium chlorate in the presence of manganese dioxide by heating. All the substances in this reaction are solid phase.

2KClO3 → 2KCl + 3O2

  • Nitric oxide is used in the Chamber process for the oxidation of sulfur dioxide to sulfur trioxide. Where the reactant sulfur dioxide oxidized by oxygen are gas phases and catalyst nitric oxide also in the gas phase.

2SO2 + O2 → 2SO3
SO3 + H2O → H2SO4

  • The decomposition of acetaldehyde catalyzed by iodine vapor produces methane and carbon monoxide.


  • Inversion of can sugar catalyzed by hydrogen ion or protons in the water solution produce glucose.

C12H22O11 + H2O → 2C6H12O6

  • Heber process of manufacture of ammonia molecule catalyzed by iron, this is the example of heterogeneous catalysis reaction.

N2 + 3H2 → 2NH3