During a chemical reaction, reactants are converted to products. The chemical reaction can be represented in a balanced chemical equation where the numbers and kind of atoms on both sides of the equations are the same.

In the above equation, 2 molecules of hydrogen react with one molecule of oxygen to form 2 molecules of water. It can also be stated that "2 moles of hydrogen molecules reacts with 1 mole of oxygen molecules to form 2 moles of water molecules". The ratio of hydrogen molecules to oxygen molecules will always be 2:1. This relationship is called stoichiometry and the whole numbers in from of the reactants and products are referred to as the stoichiometric coefficients.

For example, the stoichiometric coefficient for each species in the above equation is as follows:

1. For the hydrogen molecule, it is 2.
2. For the oxygen molecule, it is 1.
3. For the water molecule it is 2.

The stoichiometric relationship between the products and reactants can be used to in calculations. Follow the example below and then try a few problems on your own.

Example 1: Aqueous solutions of sodium hypochlorite (NaOCl), best known as household bleach are prepared by the reaction of NaOH with Cl₂. How many grams of NaOH are needed to produce 15.0g of NaOCl?

1. First, we need to convert the grams of NaOCl to moles of NaOCl. We do this using the formula weight of NaOCl.

2. Next, we will use stoichiometry to relate the moles of NaOCl to the moles of NaOH.

3. Finally, we convert moles NaOH to grams of NaOH using the formula weight of NaOH.

This problem can also be done in one single step.

Try some problems on your own.

1. How many grams of TiO₂ can be prepared from 4.30 g of TiCl₄?

1. If you react 1.30 g of BaCl₂ with 3.54 g of AgNO₃, how much silver chloride (AgCl) is produced? (Limiting Reagent Problem)