Chemical reactions convert reactants to products, whose properties differ
from those of the reactants. Chemical equations are a compact and
convenient way to represent chemical reactions. They have the general form
Reactant(s) → Product(s)
The arrow in the equation means "changes to" or
"forms." The reaction of gaseous nitrogen with hydrogen to
produce ammonia, NH
3
, is represented by the chemical equation
Although there are thousands of chemical reactions, a significant number
of them, especially those that are not organic reactions, can be
classified according to four general patterns: combination, decomposition,
displacement, and exchange.
Read more: http://www.chemistryexplained.com/Di-Fa/Equations-Chemical.html#ixzz4XjnDFUrK