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Catalysts

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The tunnel through this mountain provides a faster route for cars to get to the other side of the mountain. If a chemical reaction were like a road to the other side of a mountain, a catalyst would be like a tunnel.  

What Is a Catalyst?

A catalyst is a substance that increases the rate of a chemical reaction. The presence of a catalyst is one of several factors that influence the rate of chemical reactions. (Other factors include the temperature, concentration, and surface area of reactants.) A catalyst isn’t a reactant in the chemical reaction it speeds up. As a result, it isn’t changed or used up in the reaction, so it can go on to catalyze many more reactions.

Q: How is a catalyst like a tunnel through a mountain?

A: Like a tunnel through a mountain, a catalyst provides a faster pathway for a chemical reaction to occur.

How Catalysts Work

Catalysts interact with reactants so the reaction can occur by an alternate pathway that has a lower activation energy. Activation energy is the energy needed to start a reaction. When activation energy is lower, more reactant particles have enough energy to react so the reaction goes faster. Many catalysts work like the one in the diagram below. (You can see an animated version at the following URL.) The catalyst brings the reactants together by temporarily bonding with them. This makes it easier and quicker for the reactants to react together. Notice how the catalyst is released by the product molecule at the end of the reaction.

http://www.scs.sk.ca/cyber/elem/learningcommunity/sciences/chemistry30/curr_content/chem30/modules/module4/lesson5/explainingcatalysts.htm

Q: In the diagram above, look at the energy needed in the catalytic and non-catalytic pathways of the reaction. How does the amount of energy compare? How does this affect the reaction rate along each pathway?

A: The catalytic pathway of the reaction requires far less energy. Therefore, the reaction will occur faster by this pathway because more reactants will have enough energy to react.

Catalysts in Living Things

Chemical reactions constantly occur inside living things. Many of these reactions require catalysts so they will occur quickly enough to support life. Catalysts in living things are called enzymes. Enzymes may be extremely effective. A reaction that takes a split second to occur with an enzyme might take many years without it!

More than 1000 different enzymes are necessary for human life. Many enzymes are needed for the digestion of food. An example is amylase, which is found in the mouth and small intestine. Amylase catalyzes the breakdown of starch to sugar. You can see how it affects the rate of starch digestion in the Figure below .

Q: If you chew a starchy food such as a soda cracker for a couple of minutes, you may notice that it starts to taste slightly sweet. Why does this happen?

A: The starches in the cracker start to break down to sugars with the help of the enzyme amylase. Try this yourself and see if you can taste the reaction.

Summary

  • A catalyst is a substance that increases the rate of a chemical reaction.
  • A catalyst provides an alternate pathway for the reaction that has a lower activation energy. When activation energy is lower, more reactant particles have enough energy to react, so the reaction occurs faster.
  • Chemical reactions constantly occur inside living things, and many of them require catalysts to occur quickly enough to support life. Catalysts in living things are called enzymes.

Vocabulary

  • catalyst : Substance that increases the rate of a chemical reaction but is not changed or used up in the reaction.

Practice

At the following URL, watch the video showing a chemical reaction both with and without a catalyst. Then answer the questions below.

http://www.youtube.com/watch?v=GSCJ2EYkRqQ

  1. Write the chemical equation for the reaction that is demonstrated in the video.
  2. What chemical is used to catalyze the reaction?
  3. Describe two observations that provide evidence that the reaction has occurred after the addition of the catalyst.

Review

  1. What is a catalyst?
  2. How does a catalyst speed up a chemical reaction?
  3. What are enzymes? Why are they important?

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