Chemical equations represent the language of chemistry. When a chemist writes "A + B --> C," he's expressing a relationship between the reactants of the equation, A and B, and the product of the equation, C. This relationship is an equilibrium, although the equilibrium is often one-sided in favor of either the reactants or the products. Not every chemical equation a chemist writes represents a productive reaction, however. Learn the conventions of chemical equations to determine whether the equation you are analyzing represents a reaction.
Write the chemical equation you want to analyze; for example, the reaction of a strong acid (HCl; hydrochloric acid) and a strong base (NaOH; sodium hydroxide): "HCl(aq) + NaOH(aq) --> NaCl(aq) + H2O(l)." Note that the arrow in the equation means "yields."
Identify any chemical terms in the equation to the right of the arrow. For example, you identify NaCl (sodium chloride, or common table salt) and H2O (water).
Note that when there are chemical terms to the right of the arrow in a chemical equation, there is a reaction.
Write another chemical equation you want to analyze; for example, the combination of sodium chloride (NaCl) and calcium nitrate (Ca[NO3]2): "NaCl(aq) + Ca(NO3)2(aq) --> NR." Remember that "NR" means "no reaction."
Note that there are no chemical terms to the right of the arrow. No reaction takes place in the chemical equation you have written.