Stoichiometry

Stoichiometry is a branch of chemistry that deals with the quantitative relationships that exist between the reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers. For example, in a reaction that forms ammonia (NH₃), exactly one molecule of nitrogen (N₂) reacts with three molecules of hydrogen (H₂) to produce two molecules of NH₃:

N₂ + 3H₂ → 2NH₃

Stoichiometry can be used to calculate quantities such as the amount of products that can be produced with given reactants and percent yield (the percentage of the given reactant that is made into the product). Stoichiometry calculations can predict how elements and components diluted in a standard solution react in experimental conditions. Stoichiometry is founded on the law of conservation of mass: the mass of the reactants equals the mass of the products.

Reaction Stoichiometry describes the quantitative relationships among substances as they participate in chemical reactions. In the example above, reaction stoichiometry describes the 1:3:2 ratio of molecules of nitrogen, hydrogen, and ammonia.

Remember:
-balanced the chemical equation before solving the problem.
-what you need over what you have, where you're going over where you from.

Example:

     Consider the chemical equation:

           N₂ + 3H₂ → 2NH₃

 Q: How many moles of  H_{2 will be formed when 3.7 moles of} NH_{3 is decomposed?}

                                              

                                           _{3 moles of}  H₂

             _{3.7 moles of}  NH_{3  x  ____________  =  5.55 moles of} H₂ 

                                                    

                                                         _{2 moles of} NH₃