Example of Catalyst in Chemistry
A 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. Therefore the catalytic activity of catalysts action on the rate of the reaction by changing activation energy without effect on the equilibrium. For example, in chemistry, hydrogen ion used as a catalyst in the catalysis reaction of sugar or ester.
A chemical catalyst, therefore, provides the alternate path of lower activation energy to the reaction. This decreases in activation energy results in an increase in reaction rate and the effect 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.
An example of catalyzed reaction is the decomposition of KClO3 in presence of MnO2.
2KClO3 → 2KCl + 3O2
Catalytic Activity and Activation Energy
The catalytic reaction occurs when the activity of substance increase by lowering the activation energy of the catalyst.
Therefore in homogeneous catalysis, catalyst provides an alternative path in which the activation energy lowered. Lesser 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 mass and composition at the end of the reaction. However, the physical state like particle size or color of the catalyst maybe alter.
For example, MnO2 used in the decomposition of KClO3 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 O2 per minute from the decomposition of hydrogen peroxide. Platinium remains active even production of 10 lit of O2.
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. Hence ΔG0 remains the same 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 forwarding 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.
Catalytic Action of Catalyst
The catalytic action of catalyst is specific, thus it can not be used for every reaction. For example, MnO2 can catalyze the decomposition of KClO3 but not KNO3 and KClO4. However, the change of catalyst changes the nature of the product of the reaction.
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 enzyme chemistry, catalytic action increase with the rise of temperature but the efficiency falls down after a certain temp 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
- Homogeneous catalysis: The catalyst present in the same phase as the reacting substances.
- Heterogeneous catalysis: The catalyst is present in a different phase from the reactant.
- NO is used in the Chamber process of manufacture of H2SO4. Where the reactant SO2, O2, and catalyst NO present in the gas phase.
2SO2 + O2 → 2SO3
SO3 + H2O → H2SO4
- Decomposition of acetaldehyde catalyzed by iodine vapor.
CH3CHO → CH4 + CO
- Inversion of can sugar catalyzed by hydrogen ion
C12H22O11 + H2O → 2C6H12O6
- Heber process of manufacture of NH3 catalyzed by Fe, this is the example of heterogeneous catalysis reaction.
N2 + 3H2 → 2NH3