Effect of Catalysts on Rates of Reaction

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  • 0:02 Introduction to Catalysts
  • 1:20 How do Catalysts Work?
  • 3:35 Catalysts in Industry
  • 5:30 Biological Catalysts
  • 6:53 Lesson Summary
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Lesson Transcript
Instructor: Nicola McDougal

Nicky has taught a variety of chemistry courses at college level. Nicky has a PhD in Physical Chemistry.

In this video lesson, we will learn how catalysts speed up chemical reactions. We'll also discuss how catalysts are used in industry and consider the catalysts in our own bodies. A short quiz will test your new knowledge.

The Moffat Tunnel and Catalysts

There are parts of the USA that are very mountainous, like the Rocky Mountains in Colorado. Imagine trying to run a railroad over these steep climbs. You would think it would be impossible. Well it almost was! Amazingly, at the beginning of the 20th century, trains did attempt these climbs. There were tough gradients to deal with, and it took a lot of effort for a train to make it. The train zigzagged its way up the mountain, and the run was slow and arduous. During the winter months, it took even longer, because snow often blocked the train's path.

But in 1927, the Moffat Tunnel was built and the journey became a whole lot easier. Moffat Tunnel is one of the most famous railroad tunnels in America, and it is over six miles long. It carves its way through the Rockies and provides a much better route for the train. This new, easier route takes away the almost impossible challenge of trying to climb the mountain. Journey times can be measured in hours rather than days.

This story will help us understand just how catalysts work. Just imagine that chemical reactions are, in fact, mountains.

How Do Catalysts Work?

A catalyst is defined as a chemical substance that takes part in a chemical reaction and influences its rate without undergoing permanent change. Chemical catalysts work in exactly the same way as the Moffat Tunnel did. Catalysts offer an alternative way of getting from one place to another. It is important to notice that you are still starting and ending at the same place; you are just going an easier way to get there. So let's understand how they do this.

Here we have a diagram of a typical chemical reaction:

Chemical Reaction
Chemical Reaction

Our starting position is the reactants: hydrogen and chlorine. This is our point A. We finish at point B, the products of hydrogen chloride. The hill in the middle is the energy barrier that we have to get over to get from point A to point B.

This hill is called the activation energy, and this is the energy necessary to initiate a chemical reaction. For any reaction to happen, you have to get over this barrier. Now, you can see the hill is quite steep, just like the Rocky Mountains. It takes a lot of energy to get over it. But, take a look at the red line. This is the route you take with a catalyst. Just like the Moffat Tunnel, you can get from point A to point B much more easily using this route. The catalyzed route is an alternative way with a much lower energy cost. It has a lower activation energy, and this speeds up the reaction.

It is important to realize that the only thing catalysts change is the activation energy. You get there more quickly, but where you start and where you finish are exactly the same. So while catalysts do take part in the reaction, they are unchanged by the reaction.

To help you understand this better, think about the Moffat Tunnel. The tunnel is definitely involved in the journey from A to B because the train goes through it. It is the catalyst, because it speeds things up. But once the train has gone through, the tunnel is still the same; it is unchanged. It is ready for the next train to pass through.

Catalysts Used in Industry

So far we have learned that catalysts speed up chemical reactions by lowering the activation energy. In fact, just a small decrease in the activation energy can dramatically increase the rate of reaction. For this reason, you will find many, many catalysts used in industry.

Catalysts can be classed into two main groups. Homogenous catalysts are in the same phase as the reactants. So for example, if the reactants are in aqueous solution, so is the catalyst. Heterogeneous catalysts are in a different phase than the reactants. For example, solid catalysts are often used for speeding up aqueous or gaseous reactions.

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