Collision theory Activation energy Rate of reaction
Reactants Learning Intentions
In this topic we are learning to: zz
Explain activation energy.
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Consider how the rate of a chemical reaction can be monitored over time. Interpret a rate of reaction graph.
All substances are made up of particles. Before a chemical reaction happens, the particles in the reactants must collide with each other. This is called the collision theory.
Product
The more collisions between particles in a given time, the faster the reaction will take place.
Not every collision will result in a new product being formed. The colliding particles must have a minimum amount of energy.
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Activation energy is the energy needed to start a reaction
The minimum energy needed to start a reaction is called activation energy.
Notice the ‘hill’ in the energy profile diagrams for both exothermic and endothermic reactions (Figs. 12.2.4 and 12.2.5, page 207). This hill represents the minimum energy needed to start the reaction. The higher the barrier, the slower the reaction.
Rate of Reaction
Some reactions are slow and some reactions are fast. The rate of reaction describes how quickly a chemical reaction happens.
It is very important that scientists can control or change the rate of chemical reactions. For example, in the pharmaceutical industry scientists have to know exactly how much of their product they can make each hour, day or week.
Fast or slow?
Research the rates of the reactions below and place them in order from fastest to slowest: zz
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Wine fermenting. Baking a cake.
Dynamite exploding. Milk going sour.
Limestone rock being weathered. Iron nail rusting.
Antacid tablet relieving symptoms of heartburn. Fig. 12.3.2
