How Does a Catalyst Affect the Rate of Chemical Reactions?

Introduction

Catalysis is the process of altering the reaction rate by utilising a chemical that is not used by the reaction. As a result, it does not show any change in the total stoichiometry of the process, but it must occur in at least a single elementary process in the catalysed reaction mechanism. Although the catalysed route has smaller activation energy, the total energy shift that comes from the reaction is unaffected by the existence of a catalyst. Nonetheless, because of its smaller activation energy, a catalysed reaction has a quicker rate of reaction than an uncatalyzed reaction at a similar temperature. Because a catalyst lowers the altitude of the barrier of energy, its introduction raises both the forward & reverse reaction speeds by a similar amount.

nigerianscholars.com, Trans effect energy diagram, CC BY-SA 4.0

What is Catalysis?

• Catalysis is the change of the reaction rate, generally by the introduction of a compound that is not used throughout the reaction, in chemistry.

• Chemical reaction rates, or velocities, are governed by a number of elements, including the chemical makeup of the reactants and the ambient conditions they are subjected.

• Catalysts, the speeding of chemical processes by chemicals other than those utilised in the reactions—substances known as catalysis—is a specific phenomenon associated with the speeds of reactions that is of immense practical as well as theoretical importance.

What is a Catalyst in a Chemical Reaction?

• It is a compound that, without being used in the process, increases or decreases the pressure or temperature necessary to commence a chemical reaction. Catalysis is the process of speeding up a reaction by using a catalyst.

• Catalysts increase the effectiveness of the reaction by decreasing the Ea (activation energy), which is the amount of energy required to start the reaction. As a result, catalysts facilitate the formation and destruction of chemical bonds, resulting in new molecules and compounds.

• Catalysts allow for faster and more energy-efficient operations. Catalysts also possess a critical property called selectivity, which enables them to manage a reaction to increasing the quantity of desired product while minimising the number of unwanted by-products. They can create whole different materials with completely novel potential uses.

• Over the last few years, scientists have developed more selective catalysts for vital practical uses. The chemical industry has been transformed by strong catalysts in particular. These discoveries have led to biodegradable polymers, new medications, and more environmentally friendly fertilisers and fuels.

• Fe is used as the catalyst in Haber's process. In this process, iron is typically used as a catalyst. Iron was chosen since it helps to get a sufficient yield of a product in a much less amount of time.

What is Homogeneous Catalysis?

• When the catalyst, as well as the reacting chemicals, are found in the same phase of matter, generally as a liquid or a gas the reactions are considered homogeneous catalysis.

• In the lead chamber method for manufacturing sulphuric, nitrogen oxides function as catalysts for the oxidation of sulphur dioxide, an example of catalytic reactions in which the reactants, as well as catalysts, are gases.

• Some gas reactions, such as the slow reaction of O₂ and CO under dry environments, are catalysed by H₂ O residues.

• SO₃ is formed via the oxidation of sulphur dioxide with molecular oxygen in the vicinity of nitrogen oxides as a catalyst.

  $$\mathrm{O_2 (g)+2SO_2 (g)→2SO_3 (g)}$$

What is Heterogeneous Catalysis?

• There are several known catalytic reactions in which the catalyst, as well as the reacting substance, are not in a similar phase. This is referred to as heterogeneous catalysis.

• They involve reactions at the top surface of a solid catalyst between liquids, gases, or even both.

• Because the surface is where the reaction takes place, it is often used in methods in metal gauzes, finely split metals, metals integrated into supporting matrices, & films of metals and used in current heterogeneous catalysis to provide a high surface area for one unit of catalyst.

• Metals are either utilised directly or transformed into sulphides, oxides, or halides.

• Sulphur dioxide reacted to SO₃ in the vicinity of Platinum.

  $$\mathrm{3SO_2 (g)→2SO_3 (g)}$$

  The catalyst is solid in this case, whereas the reactant is gaseous.

How Does a Catalyst Affect the Rate of Chemical Reactions?

• A proper catalyst can be utilised to increase the reaction rate. A catalyst is a material that accelerates a chemical process but is not consumed. It gives lower activation energy in alternative chemical routes.

• To enhance the speed of reaction between a high quantity of precursors, just a very little quantity of catalyst is needed.

  • A catalyst is very specific.

  • Catalysts are not always available for every reaction.

• The catalyst reduces the energy of the reaction's transition state. Because the activation energy is the difference between the reactant energy and the transition state energy, decreasing the transition state energy reduces the activation energy as well.

• For both the uncatalyzed and catalysed reactions, the energy of the products and reactants are the same. As a result, adding the enzyme does not influence the total energy liberated during the process. This underscores a key point: the kinetics of a reaction, i.e., reaction rate, is not directly connected to the process's thermodynamics.

Emma Ambrogi, Catalyst Energy Diagram, CC BY-SA 4.0

Conclusion

It can be concluded that catalysis is the technique of boosting the chemical reaction rate by using a catalyst. Catalysts are not used in the reaction. If the reaction is fast as well as the catalyst recycles quickly, relatively little catalyst is frequently required; surface area, mixing & temperature are all critical variables in the rate of reaction. Catalysts usually interact with 1 or more reactants to generate intermediates that then yield the ultimate product of the reaction, renewing the catalyst in the reaction.

FAQs

1. What do you mean by adsorption?

Adsorption is the concentration of molecules on the surface of a liquid or liquid instead of in its bulk.

2. What do you mean poisons and promoters?

Promoters are compounds that improve catalytic efficiency. Molybdenum, for instance, is used as a promoter to boost the activity of the catalyst Fe in Haber's ammonia production process.

Poisons are compounds that inhibit the catalyst's function. Palladium, for instance, is employed as a catalyst in the Rosenmund process.

3. Explain the terms sorption and desorption.

Desorption is described as the removal of adsorbed substances from an adsorbed surface.

Sorption is described as the simultaneous adsorption and absorption of two substances.

4. What characteristics distinguish enzymes as biocatalysts?

Enzymes that catalyse a range of reactions linked to natural processes that occur in the bodies of both plants and animals to sustain life processes are known as biocatalysts.

5. Is nickel used as a catalyst?

Due to their propensity to break C-C bonds, Ni-based catalysts are the most commonly used in reforming reactions. Due to its capacity to tolerate the reaction environments, nickel has often been supported onto alumina.