Stoichiometry Chapter 12

Section 1 - The Arithmetic of Equations Introduction More than 3000 cocoons are needed to produce enough silk to make just one elegant Japanese kimono. Like silk manufacturers, chemists must know how much reactant they need to make a certain amount of product. Determining the quantities of reactants and products in a reaction requires a balanced chemical equation.

1. Using Everyday Equations 12.1 1. Using Everyday Equations A balanced chemical equation provides the same kind of quantitative information that a recipe does. For example, an equation can represent the manufacturing of a single tricycle. Assume the major components of the tricycle frame (F), seat (S), the wheels (W), the handlebars (H), and the pedals (P). The finished tricycle would have the formula FSW3HP2 A cookie recipe tells you the number of cookies that you can expect to make from the listed amounts of ingredients. Using Models How can you express a cookie recipe as a balanced equation?

2. Using Balanced Chemical Equations Nearly everything you use is manufactured from chemicals For example: soaps, shampoos & conditioners, CDs, cosmetics, medicines, & clothes. In manufacturing items, the cost of making them cannot be greater than the price at which they are sold, otherwise, the manufacturer will not make a profit Therefore, the chemical processes used in manufacturing must be carried out economically.

Using Balanced Chemical Equations (cont.) Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction. When you know the quantity of one substance in a reaction, you can calculate the quantity of any other substance. The calculation of quantities in chemical reactions is a subject of chemistry called stoichiometry. It allows chemists to tally the amounts of reactants and products using ratios of moles or particles.

Using Balanced Chemical Equations (cont.) For Example: Step 1: Using Balanced Chemical Equations (cont.)

Using Balanced Chemical Equations (cont.) Step 2: Step 3:

3. Interpreting Chemical Equations The balanced equation tells you the relative amounts of reactants and product in the reaction. A balanced chemical equation can be interpreted in terms of different quantities, including numbers of atoms, molecules, or moles; mass; and volume. Number of Atoms At the atomic level, a balanced equation indicates the number and type of each atom

Interpreting Chemical Equations (cont.) 12.1 Interpreting Chemical Equations (cont.) Number of Molecules The balanced equation indicates the ratio of one molecule to another. The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

Interpreting Chemical Equations (cont.) Moles The coefficients of a balanced chemical equation indicate the relative numbers of moles of reactants and products in a chemical reaction. Using this number you can calculate amounts of reactants and products

Interpreting Chemical Equations (cont.) 12.1 Interpreting Chemical Equations (cont.) Mass A balanced chemical equation obeys the law of conservation of mass The total mass of the atoms in the reactions does not change. The total number of grams of reactants equals the total number of grams of the products The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

Interpreting Chemical Equations (cont.) 12.1 Interpreting Chemical Equations (cont.) Volume If you assume standard temperature and pressure, the equation also tells you how much volume a gas occupies. The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

4. Mass Conservation in Chemical Reactions 12.1 4. Mass Conservation in Chemical Reactions Mass and atoms are conserved in every chemical reaction. Molecules, formula units, moles, and volumes may not be conserved. Example:

Mass Conservation in Chemical Reactions (cont.) Step 1:

Mass Conservation in Chemical Reactions (cont.) Step 2:

END OF SECTION 1