Collision Theory - The collision theory states that chemical reactions occur when molecules collide. The energy required to start a reaction is called the minimum energy of activation. There are four general types of chemical reactions: rearrangement, synthesis, degradation, and displacement.
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| Collision Theory |
Today is a very exciting time in chemistry, since scientists can actually move atoms and also image the progress of chemical reactions. But, what are chemical reactions?
Simply stated, chemical reactions involve breaking and reforming chemical bonds. In order to do this, energy is required, and the amount of energy available in the system determines whether or not a reaction will occur. For example, if you assume that all atoms, ions, and molecules are constantly moving, then a chemical reaction can occur when they collide with one another. This is what happens when two atoms of hydrogen unite with a molecule of oxygen to form water (H2O). Chemists call this explanation the collision theory.
For example, when you played with your old chemistry set you learned that if you simply mixed two chemicals together, it usually took a long time for a chemical reaction to occur. However, if you heated the mixture (which is one way to put energy into a system), the reaction proceeded much more quickly. Basically, according to the collision theory, the addition of heat increased the speed at which the atoms and molecules were moving, and thus increased the likelihood that they would collide and react. (There are other ways to add energy to a material by shaking or increasing pressure, for instance but heat is the one that is most common, especially in biological processes.)
Adding just a little heat will not necessarily get results. Before a reaction can occur, a certain minimum amount of energy must be added, which chemists call the minimum energy of activation. What is more, the level of the minimum energy of activation depends on the substances involved. For instance, if you light a match and toss it into a small pan of gasoline, you provide enough energy (in the form of heat) to combine the gasoline and oxygen to form carbon dioxide, water, and a tremendous amount of liberated energy (in other words, the explosion will be something to see). However, if you fill the pan with another liquid, such as plain water, the lighted match will have no effect. (Source: Avila, Vernon L. Biology : Investigating Life On Earth Jones and Bartlett/Bookmark Series in Biology Page 52)
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