Introduction to Catalysis

Most reactions that occur in nature require a lot of time for completion.

In Order to speed up the reaction, a substance called CATALYST has to be added.

Catalysis is the process in which the rate of any reaction is altered, by addition of a catalyst.

Generally, the catalyst does not take part in the reaction. So, it remains chemically unchanged.

In this process, we can increase or decrease the rate of the chemical reaction.

But generally, catalysis process is used to increase the rate of reaction.

Now we will see how catalysis process increases or decreases the rate of reaction.

All chemical reaction requires some energy to activate the reaction, and that required energy is known as Activation energy.

And catalysis process reduces that activation energy of the reaction

And thus reaction starts earlier and takes place with a faster rate

Let us understand the mechanism of catalysis with an example.

The following diagram shows an energy diagram for the reaction between carbon dioxide () and water ()

In this reaction, an enzyme is added as a catalyst to form the product Carbonic acid ()

Here the reaction with a catalyst is indicated by the blue line and the uncatalyzed reaction is indicated by the red line

It is evident that catalyst lowers the activation energy of the transition state for the reaction.

Since catalyst lowered the activation energy the reaction will start earlier and take place with a faster rate.

Here we can notice that energies of the reactant and product are the same for both catalyzed and uncatalyzed.

Therefore we can conclude that overall energy released during the reaction does not change when we add the catalyst.

Now we will see the types of catalyst.

Depending upon whether the phase of reactant and catalyst is the same or not, the catalyst is divide into two types.

The first type of catalyst is Homogeneous catalyst

If the phase of the reactant and the catalyst is same then the catalyst is known as Homogeneous catalyst.

Let us understand homogenous catalyst with an example.

Here is oxidised to by in the presence of catalyst

In this reaction, reactants and are in gaseous form and also catalyst is in gaseous form.

So, here both reactant and product are in the same phase that is in gaseous form so, here is Homogeneous catalyst.

Let’s study about other type of catalyst that is Heterogeneous catalyst.

If the phase of reactants and the catalyst is not the same, that type of catalyst is known as a Heterogeneous catalyst.

Most of the heterogeneous catalyst are solids that act on substrates in a liquid or gaseous reaction mixture.

Let us understand heterogeneous catalyst with an example.

In the below reaction ammonia is synthesized from and using iron as catalyst

Here reactants and are in gaseous phase while catalyst is in solid phase.

Hence reactants and catalyst are in different phase so here iron (Fe) is the heterogeneous catalyst.

Revision.

Catalyst is a substance added to increase the rate of the reaction.

Chemical reactions require some energy to activate the reaction, and that required energy is known as Activation energy.

Overall energy released during the reaction does not change on the addition of the catalyst.