Whenever molecules rearrange their atoms during a chemical change, energy is either released or absorbed. How much energy depends on how fast the atoms rearrange themselves. When iron rusts, for example, oxygen in the air combines with iron atoms. This reaction is known as oxidation. The reaction releases energy, but because the oxidation rate is so slow, the temperature of the rusting area increases just slightly—only by about one degree F.
Under certain conditions, though, the oxidation rate of some materials can be very fast and generate a great deal of heat. If this heat cannot dissipate faster than it is created, then combustion results.
To find out more about combustion, select one of the following.