


•  


•                


Chapter 21


Key terms activation energy rate of reaction temperature concentration


RATES OF REACTIONS


In this chapter, you will learn to: / explain activation energy in relation to a chemical reaction


surface area catalyst biochemical reaction


/ investigate factors that affect the rate of reaction / draw a rate of reaction graph / describe how common gases are produced in the laboratory


/ explain what a biochemical reaction is and give examples of biochemical reactions.


Activation energy


We know that chemical reactions take place when two or more substances (called reactants) combine to form a new substance (known as a product). Before a chemical reaction can happen, the particles in the reactants must collide with each other. The more collisions between particles in a given time, the faster the reaction will take place.


For a new product to form, the colliding particles must have a minimum amount of energy. The minimum energy needed to start a chemical reaction is called activation energy.


Rate of reaction


Some chemical reactions are fast and some are slow. For example, a firework exploding is a reaction that takes place quickly, while an iron nail rusting is a reaction that takes place slowly. The rate of reaction is the measure of how quickly a chemical reaction happens.


:Fig. 21.1 A firework exploding is a fast rate of reaction :Fig. 21.2 An iron nail rusting is a slow rate of reaction


It is important that scientists know the rate of chemical reactions. For example, this helps the pharmaceutical industry to understand exactly how much of their product they can make each hour, day and week.


Elements of Science 199


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