Positive Catalysts

Catalysts are substances, when added in any chemical reaction, alter or change the rate of an ongoing chemical reaction. In other words, catalysts are rate-changing factors of any chemical reaction. Catalysts are of two types–positive and negative. 

Positive catalysts change the reaction rate by increasing the reaction rate, and negative catalysts change any chemical reaction by decreasing the reaction rate.

Positive catalysts

From the definition of catalysts, we know that catalysts change the actual ongoing chemical reaction rate. The term ‘positive catalysts’ suggests that it positively impacts the rate of any chemical reaction by increasing the rate of that ongoing reaction. In the reversible reaction, a positive catalyst will not alter the position of equilibrium but try to attain the equilibrium state of the reaction in a shorter time.

Working of positive catalysts 

The reactant molecules require a minimum amount of energy to reach the threshold energy point to complete any chemical reaction. The threshold energy point is when an activated complex species is formed. Here, partial bonds of reactant and partial bonds of a product are present or mixed bonds of reactant and product are present; this activated complex species then finally converts into the product of the reaction. 

The required amount of energy is known as activation energy to reach the threshold energy point. Suppose any catalysts are present in any chemical reaction. In that case, it provides an alternate path to the reactant molecules by providing less activation energy and a different kind of transition state than the original activation energy for the ongoing chemical reaction. Finally, it increases the rate of that given chemical reaction.

In the process of a catalysed chemical reaction, catalysts are not purely involved in the reaction, it only provides the alternate path by sometimes providing its surface area to the reactant to get reacted, or itself get reacted with the reactant to form the intermediate species, and after the completion of reaction, we get the same product and pure catalyst as I put in the initial duration of the reaction.                                         

Examples of catalysts

• Enzymes come under the category of positive catalyst and are known as biological catalyst as they increase the rate of any chemical reaction within the human body as follows:

H2CO3 (aq)  ↔  H2O(l) + CO2(g)

• In the above chemical reaction, carbonic anhydrase  (H2CO3) is the biological catalyst that increases the diffusion rate of carbon dioxide (CO2) from the blood towards the lungs as we can exhale the carbon dioxide gas by reaching the equilibrium state very quickly.

• Potassium permanganate (KMnO4) is also a catalyst that increases the rate of decomposition chemical reaction of hydrogen peroxide (H2O2), which in turn converts into oxygen gas (O2) and water (H2O) by increasing the temperature of the reaction. Temperature increases, increasing the collision rate of reactant molecules and the reaction rate.

• Many transition metals also behave as catalysts, increasing the rate of many chemical reactions like platinum (Pt). Platinum is used in automobiles as a converter. 

• Platinum black is also used as a positive catalyst as it increases the possibility of the combination of oxygen gas (O2) and hydrogen gas (H2) to form water molecules.

 2H2  +  O2  —(Pt)–  2H2O

• Nitrogen oxide (NO) is another positive catalyst that increases the chemical reaction rate of oxidation of SO2 into SO3.

• Manganese dioxide is also a positive catalyst as it increases the rate of decomposition of potassium chlorate (KClO3) into potassium chloride (KCl) and oxygen gas, so the obtained oxygen gas (O2) will liberate.

2KClO3 (s) –−−(∆, MnO2)−−→ 2KCl(s) + 3O2(g)

• Iron (Fe) is a positive catalyst in the ammonia synthesis process.

• Zeolites are a positive catalyst in the petroleum cracking process.

• Nickel, palladium, and platinum are positive catalysts in the hydrogenation process of unsaturated hydrocarbons.

Conclusion

A positive catalyst is a substance that increases the rate of any ongoing chemical reaction by only being involved in the reaction and without being consumed by the reaction species. The rate of a chemical reaction in the presence of a catalyst increases because of the lowered activation energy of the reactants involved.