READ: Catalysts
READ: Catalysts
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.
Chemical reactions require a certain amount of energy just to get started. This energy is called activation energy. For example, activation energy is needed to start a car engine. Turning the key causes a spark that activates the burning of gasoline in the engine. The combustion of gas won’t occur without the spark of energy to begin the reaction.
Q: Why is activation energy needed? Why won’t a reaction occur without it?
A: A reaction won’t occur unless atoms or molecules of reactants come together. This happens only if the particles are moving, and movement takes energy. Often, reactants have to overcome forces that push them apart. This takes energy as well. Still more energy is needed to start breaking bonds in reactants.
The addition of a catalyst (a substance that increases the rate of a chemical reaction without being used up) is another way to speed up a reaction. Catalystslower the activation energy for a reaction. A catalyst isn’t a reactant in the chemical reaction, but it speeds the reaction 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.
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. The catalyst brings the reactants together by temporarily bonding with them. This makes it easier and quicker for the reactants to react together. The catalyst is released by the product molecule at the end of the reaction.
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 can 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.
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
- The collision theory explains why reactions occur between atoms, ions, and/or molecules and allows us to predict what conditions are necessary for a successful reaction to take place.
- With increasing temperature, the kinetic energy of the particles and the number of particles with energy greater than the activation energy increases.
- How fast a chemical reaction occurs is called the reaction rate.
- Several factors affect the rate of a chemical reaction, including the temperature, concentration, and surface area of reactants, and the presence of a catalyst.
- 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.
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