Catalyst in Chemistry

A catalyst is a substance that overall changes the rate of reaction without being consumed in a reaction. In Chemistry, catalysts are widely used to enhance the rate of any chemical reaction without changing the product. The name catalyst was given by Berzelius in 1835. A large number of catalytic reactions are known in chemistry and chemical technology. 

A famous chemist Ostwald defined a catalyst as a substance that alters a chemical reaction’s rate without undergoing any chemical changes. According to him, the alteration is caused either by increasing or decreasing the rate of the chemical reaction. But today, catalysts are widely used for only enhancing the reaction rate. Exceptionally they are used for declining the initial reaction rate. 

What is a catalyst?

When the rate of a given chemical reaction is not considerably altered by changing various conditions such as temperature, concentration, pH, etc., of the reactants, new substances are brought which are not directly involved in the reaction and are mixed. And they finally made alterations in the given chemical reaction. Such new substances are known as a catalyst. 

The process by which a catalyst changes the reaction rate without being involved in it is known as catalysis. Based on how catalysts altered the rate of reactions, they are divided into the following types.

Positive catalyst: 

Those substances that accelerate the rate of a chemical reaction without undergoing any chemical change are called Positive catalysts, and the phenomena are known as positive catalysts.

Negative catalyst:

Those substances which decline or retards the rate of a chemical reaction are known as Negative catalyst, and the phenomenon is termed negative catalysis.

Auto catalyst:

Those substances produced in the chemical reaction and act as catalysts are called Auto catalysts, and the phenomenon is known as Autocatalysis. 

How does a catalyst work?

Catalysts work so that it may speed up the reaction rate by lowering the activation energy, or it may change the whole reaction mechanism. This is more commonly seen in the field of chemistry. 

On the other hand, catalysts may also slow down the reaction rate by increasing the activation energy or changing the whole reaction mechanism. This is very rarely seen. 

By looking at these two points, a relation between the activation energy and the rate of the chemical reaction is generated, and that is:- The rate of a chemical reaction is inversely proportional to the activation energy of this specific reaction. 

Examples of a catalyst:

Acid-base catalyst:

There are two types of acid-base catalysis found. The first is which reaction rate is proportional to the concentration of H+ or OH¯. This is known as specific catalysis. The second type is called general catalysis.

In acid catalysis, the catalyst is an H+ ion, while in base catalysis, the catalyst is a OH¯ ion. 

Homogeneous catalyst:

These catalysts are in the same phase with respect to reactants and products. This means that if the catalyst is liquid in form, the reactants and the product are also in a liquid form. 

For example: CH3COOCH3(l) + H2O(l) CH3COOH(l) + CH3OH(l).

In this example, the catalyst HCl is in a liquid state. And, the reactant and the product are also in a liquid state. 

Heterogeneous catalyst:

These are the catalysts in a different state with respect to reactants and products. This means that if the catalyst is in the liquid state, the reactants and the products are other than the liquid state. 

For example, catalytic converter in gasoline. 

Catalytic converters are usually transitioning metal catalysts wrapped along with solid-phase support. They react with the car’s exhaust stream, which is gaseous in state and leads to an increase in the overall reaction rate, resulting in less toxic products from pollutants. 

Conclusion

Catalysts are those substances that alter the rate of a chemical reaction without being consumed in it. Catalysts perform their function by lowering the activation energy or changing the mechanism of chemical reactions. There are generally three types of catalysts based on their functions. They are Positive catalysts, negative catalysts, and autocatalysts. Enzymes also act as catalysts specifically in biochemical reactions. Common examples of catalysts include acid-base, homogenous, and heterogeneous catalysts.