Chemical Catalyst in Chemistry
Chemical catalyst is a foreign substance that increases the speed of the reaction by lowering activation energy without change at the end of the chemical or biological process. Therefore, a catalyst in chemistry can be simply defined as a substance that enhances the speed of chemical reaction itself remaining unaltered in inactivity, mass, and chemical composition. The catalyst plays an important role in many chemical and real-life biological processes and work to find the alternate path where activation energy decreases but kinetics reaction rate increases. The phenomenon where catalysts show its activity define as the catalysis reaction (homogeneous or heterogeneous) in chemistry. For example, hydrogen ion acts as a positive catalyst in the hydrolysis of ester or sugar without effect on chemical equilibrium.
Sometimes the foreign substance slows down the speed of the chemical synthesis process or even stops the reaction is called a negative catalyst. But such common definition does not fully satisfy for negative catalysts in chemistry because negative catalyst sometimes changes the chemical process permanently. Therefore, such substances in chemistry are properly called an inhibitor. For example, sulfuric acid acts as an inhibitor in the decomposition of hydrogen peroxide.
Effect of Catalyst on Chemical Reaction
The catalyst uses in the catalytic reaction has some common and definite characteristics in chemistry or chemical science. The most important characteristics of the catalyst remain unchanged in the molecular mass, density, concentration, and chemical formula of constitute elements at the end of the reaction. However, the physical state of chemicals like particle size or color of the chemical catalyst maybe alter. For example, manganese dioxide uses for the decomposition of potassium chlorate becomes finely divided powder after the chemical reaction is completed.
A catalyst can increase the rate or speed of chemical reactions but can not start a reaction or affect the equilibrium of the reaction. This meaning the catalyst itself is not consumed during the chemical 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. But the platinum elements remain active even production of 10 lit of oxygen in catalysis reaction.
How do Catalysts Effect Equilibrium?
The catalyst does not affect the final state of equilibrium derived from Van’t Hoff equation, ΔG0 = – RT lnk, where k = equilibrium constant. Since the catalysts do not contribute any energy to the system to increases the free energy but increase the entropy of the system. The thermodynamics definition or equation of free energy shows the fact that the catalyst does not change the free energy and equilibrium constant of the chemical reaction.
The equilibrium constant (k) = k1/k2, where k1 and k2 = rate of forward and backward reaction. Therefore, if the catalyst increases the rate of the forward process or k1 increases, to keep k constant, k2 also increases to the same extent. Thus catalysts enhancing the rate of both types like forward and backward reaction, which helps to attain equilibrium more quickly but it does not affect the equilibrium according to the Le Chatelier principle.
Catalytic Action of Catalyst
From the definition and example, catalysts play a specific role for a specific catalytic reaction in science but we can not be used the same common catalyst for every chemical process. For example, manganese dioxide can catalyze the decomposition of potassium chlorate but not potassium nitrate. However, the change of catalyst define the nature of the chemical product of the reaction in chemistry. For example, carbon monoxide and hydrogen in the presence of nickel catalyst produce methane but in the presence of zinc oxide produce methyl alcohol molecule.
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 or role of the natural catalyst like enzyme is most marked in chemical science and biology. In biological catalysis reaction, the catalytic action of enzyme increase with the rise of specific heat but the efficiency falls after a certain temperature due to the coagulation of the enzyme.
Types of Catalyst in Chemical Reaction
In real life, the most common example of catalyst and catalyzed chemical reactions are classified into two groups or types like homogeneous and heterogeneous in chemistry. In homogeneous types of catalysis reaction, the catalyst forms a single phase with the reactants like nitric oxide in the oxidation of sulfur dioxide in the industrial chamber process or acid-catalyzed hydrolysis of the ester. But in heterogeneous catalysis, the chemical catalyst and reagents form separate phases and often the surface or interface is responsible for the catalytic properties.
Homogeneous Catalysis in Chemistry
Many homogeneous catalyzed reactions have been studied in the gas phase and liquid phase. The most common examples of such catalysis chemical reactions (gas phase), the function of the catalyst like nitric oxide in the oxidation of carbon monoxide to dioxide or decomposition of nitrous oxide to nitrogen and oxygen, iodine vapour use as catalysts for the decomposition of ethers or acetaldehyde. The reaction rate in homogeneous catalysis reaction is invariably proportional to the concentration of the catalyst.
Heterogeneous Catalysis Reaction
Heterogeneous catalysis reactions mean, a solid serve as a catalyst and the reactants are gaseous in most cases or liquid in other where one or more of these reactants absorbed on the surface of the solid. Therefore, the surface provides an alternative path for lowering activation energy or accelerate the reaction rate. In most of the reactions, the heat of adsorption increases the activation energy of the reactant, and the equilibrium reaches easily. The reaction of the solid surface catalyst consisting of four consecutive chemical steps like diffusion, adsorption, the reaction on the surface to form intermediate, and desorption or diffusion of products from the bulk to the surface. But the diffusion and desorption process is very rapid and does not play any important role in hetergenious catalysis reaction.
The catalytic function of surfaces of catalyst are specific in nature and different catalytic element are effective for the different catalytic reaction. For examples in learning chemistry, transition metal chemical surfaces like nickel (Ni) and copper (Cu) are the very good list of heterogeneous catalysts for the hydrogenation of olefin but alumina is a suitable catalyst for the synthesis of hydrocarbon from a secondary alcohol. These due to the facts that hydrogen is strongly absorbed by nickel or copper catalysts surface but water molecules are strongly absorbed by the alumina catalyst or chemical surface.