How Do Catalysts Work?

by Carson

Have you wondered why your chemical reaction is so slow? Well, if you add a suitable catalyst, it can help speed the reaction up by decreasing the activation energy needed to start a reaction. And these catalysts play a crucial role in maintaining the metabolism that keeps you alive. Today, we’ll explain how catalysts work in this article.

But What is Activation Energy?

Imagine that you have a hill in front of you. You want to roll the ball to the bottom of the hill on the other side, which is lower in altitude than where you are now. But first, you will need to roll the ball up to the top of the hill, and it takes energy to do that. That energy you need to travel to the top of the hill is the activation energy.

Once it gets to the top, the ball, with its own momentum, will roll down the other side of the hill until it reaches the lowest point.

Chemicals in reactions behave the same way. Basically, every combination of compounds has its potential energy level. When they react, they first go through an unstable transition state that increases the energy level of the reactants. That is the top of the “hill” regarding chemical reactions. Once that state is reached, it will kickstart the chemical reaction that produces the products on the other side of the hill.

The shape and height of that “hill” determine how much energy is required to start the reaction and how quickly it can spontaneously occur. Catalysts introduce intermediate unstable states to the reaction, but the tops of the “hills” are much lower than in the uncatalyzed reaction. Thus, they provide alternate pathways for the reaction to occur much faster.

Catalytic Cycles

Catalysts go through catalytic cycles when they speed up the reaction. Basically, in the catalytic cycle, catalysts provide an alternate pathway for the reaction with a lower activation energy. The products can thus be generated more quickly. Suppose the original reaction, with a higher activation energy, is X + Y → Z. But with a catalyst involved (denoted as C), here is one of the possible catalytic cycles. (Note that there are indeed other possibilities, such as the actual cycles listed below, but they look pretty similar.)

X + C  → D
D + Y  → C + Z

Note that the net reaction is still the same (X + Y → Z). Even though the catalyst reacts to form other intermediate products, the catalyst restores itself after the reaction.

Examples of Catalysts

One of the examples of catalytic reactions we will mention appears in the atmosphere’s ozone layer. When chlorine is released into the ozone layer, it can turn ozone molecules and (nearby oxygen atoms) into oxygen molecules quickly, playing a role in the depletion of the ozone layer. Here is the catalytic cycle:

Cl + O3 -> ClO + O2
ClO + O -> Cl + O2

The base reaction is O3 + O -> 2O2. Usually, when ozone (O3) gets hit by ultraviolet rays, it splits into O and O2. The presence of chlorine atoms can use the singular oxygen atoms to split ozone into the more stable oxygen diatomic molecule. That can contribute greatly to the depletion of ozone from the ozone layer.

Moreover, transition metals can also act as catalysts. They can show different oxidation states, which is the charge on the atom if the bond is completely ionic. For example, calcium usually shows an oxidation state of +2 because it tends to withdraw its two valence electrons to react with other chemicals. However, transition metals can have different oxidation states, such as iron, which has either a +2 or a +3 oxidation state, removing 2 or 3 electrons respectively. This means that they have a greater flexibility in forming intermediate compounds, and are thus more likely to be efficient catalysts.

Enzymes also speed up reactions that keep us alive in biological processes. They are proteins that arrange themselves in a specific way so that they can react with some specific chemicals. They happen to provide an alternate pathway for a reaction that is much faster and takes less energy. This kind of catalytic function of enzymes is essential for maintaining important biological processes, such as respiration and digestion. Otherwise, these basic functions would be so slow that they almost stop working.


In this article, we’ve discussed how catalysts work and the examples where we can see catalysts in daily life. These catalysts work by providing another pathway for a reaction that takes less energy to activate, and often allows it to proceed at a higher speed. If you have any suggestions or improvements to this article, please leave them in the comments below.

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