Stoichiometry and Balanced Equations
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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.
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
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.
For Example: • Step 1: Using Balanced Chemical Equations (cont.)
Step 2: Using Balanced Chemical Equations (cont.) • 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
12.1 Interpreting Chemical Equations (cont.) • Number of Molecules • The balanced equation indicates the ratio of one molecule to another.
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
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.
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:
Step 2: Mass Conservation in Chemical Reactions (cont.)
