How does a catalyst increase the rate of reaction?
A catalyst increases the rates of chemical reactions by decreasing the activation energy or energy barrier which either delays or prevents a reaction occurring.
When the activation energy is high, reactions delay occurring because.it takes a lot of frequency of collisions to equal or overcome the activation energy.
Studying and monitoring how fast or slow a reaction occur is a part of a reaction rate in chemistry kinetics.
Chemical kinetics otherwise known as reaction kinetics is responsible or deals with the rate of chemical reaction and it is vital to mention that there are certain factors that affects rates of chemical reaction.
Actually, there are about six factors that affect rates of chemical reaction; Temperature, Pressure, Concentration, Surface area, effect of light and effect of a catalyst.
It is important to also understand the full chemistry of a catalyst in chemical reactions because it will give us a full grip of why some reactions are required to be catalyzed.
I have explained how these six factors affect rates of chemical reaction but I am going to talk a little more on how a catalyst affect the rate of chemical reaction.
Please remember that the effect of a catalyst could be positive or negative. As a matter of fact. a positive catalyst is called a promoter while a negative catalyst is called an inhibitor.
How does catalyst increase the rate of reaction?
A positive catalyst increases the rate of a chemical reaction by decreasing the activation energy or energy barrier.
Activation energy must be equaled or overcome before chemical reactions will occur.
A catalyst increases the rate of reaction by decreasing the activation energy creating an alternative pathway of reduced activation energy for chemical reaction to follow.
It is important to mention that chemical reactions with high activation energy occur with difficulty while chemical reactions with low activation energy do occur with ease.
This can be further explained with examples, for example if the activation energy it will take A and B to produce C is 40J.
If you add a positive catalyst, the catalyst will provide an alternative pathway (you will see it from the graph below) of reduced energy barrier simply by decreasing the activation energy to lower energy like 20J thereby making the reaction to occur faster.
Effect of catalyst on Activation energy graph
When the activation energy is high, reactant particles struggle and collide to generate energy that must be at least equal to the energy barrier.
Reactant particles generating effective collisions to reach or overcome activation energy may take a little while but to help the reactant particles we can introduce a catalyst which will then decrease the activation energy thus hastening the rate of chemical reactions.
Even in biological systems enzymes increases the rate of chemical reaction since an enzyme is a biological catalyst.
What does a Catalyst do?
Ultimately a catalyst do decrease the activation energy and thus speeds up or increase the rates of chemical reactions.
So A catalyst speeds up the rate of a chemical reaction saving time and making products to be formed faster.
There are certain other properties of a catalyst that we should also take note;
- A catalyst is specific in function
By this we mean that a catalyst can actually increase the rate of a specified reaction though catalyst increase rate chemical reactions in general. A particular catalyst may serve as inhibitor or contaminant when used in a reaction that is known to speed up.
For example finely divide iron serve as catalyst in the Haber process for the manufacture of ammonia while vanadium V oxide serve as catalyst in the contact process for the manufactiure of sulphuric acid.
It will be wrong to assume that since iron is a catalyst, it can increase all chemical reactions and then used it in contact process.
2. A catalyst does not affect equilibrium position
We know that chemical equilibrium in chemistry exists when the rate of forward reaction equals the rate of backward reaction.
At this stage, an equilibrium position is actually established, though some reversible reactions in equilibrium could be catalyzed. However a catalyst do not alter the equilibrium position i.e shift the equilibrium position to the left or right.
3. A catalyst do not initiate a chemical reaction
This is simply saying that a catalyst is not one of the reactants and thus do not participate in a chemical reaction.
4. A catalyst remains chemically unchanged at the end of reaction
A catalyst is not consumed nor decreased in the chemically reactions but remains chemically unchanged at the end of reactions.
In conclusion, it is pertinent to mention that though chemical reactions depend on the six factors mentioned in this article, the factors in turn are governed by three parameters.
These parameters are frequency of collision, average kinetic energy of particles and activation energy.
A catalyst only affects the activation energy otherwise called the energy barrier while other factors depend on frequency of collision and average kinetic energy of particles.
