t react
             with each other are related (14 grams of nitrogen reacted with
             exactly three grams of hydrogen, eight grams of oxygen reacted to
             Amedeo Avogadro also added to the understanding of chemical
             reactions. He said that all gasses at the same pressure, volume
             and temperature contain the same number of particles. This idea
             took a long time to be accepted. His ideas lead to the
             subscripts used in the formulas for gasses.
             From the work of these and many other chemists, we now have
             a mostly complete knowledge of chemical reactions. There are now
             many classification systems to classify the different types of
             reactions. These include decomposition, polymerization, chain
             reactions, substitute reactions, elimination reactions, addition
             reactions, ionic reactions, and oxidation-reduction reactions.
             Decomposition reactions are reactions in which a substance
             breaks into smaller parts. As an example, ammonium carbonate
             will decompose into ammonia, carbon dioxide, and water.
             Polymerization reactions are reactions in which simpler
             substances combine to form a complex substance. The thing that
             makes this reaction unusual is that the final product is composed
             of hundreds of the simpler reagent (a substance that contributes
             to a chemical reaction) species. One example is the
             polymerization of terephthalic acid with ethylene glycol to form
             the polymer called Dacron, a fibre, or Mylar, in sheet form:
             nH2OC(C6H4)CO2H + nHOCH2CH2OH -* [...OC(C6H4)CO2CH2CH2O...]n
             in which n is a large number of moles. A chain reaction is a
             series of smaller reactions in which the previous reaction forms
             ...