DESCRIBING CHEMICAL REACTIONS

Brief Terminology Chemical Reaction What actually happens in reality. Chemical Equation Represents the reaction. (What we write down.)

Parts of Chemical Equation This reads:Two moles of H 2 combine with one mole of O 2 to produce two moles of H 2 O. (The arrows are like equals sign in math, except it tells you what are the reactants (react) and what are the products (produced). Coefficients:tells you how many moles of compounds (whole number appears in front of chemical ) Subscripts:tells you how many of the preceding atoms you have in each compound (assume 1....) Reactants:left side of the equation; Products: right side 2H 2 + O 2 → 2H 2 O

Chemical Reactions Have Physical Indications 1.Produce Energy (e.g., heat & light) 3. Produce Gas 4. Form Precipitate 2. Color Change

Chemical Reactions follow the Law of Conservation of Mass 1. The equation must represent the known facts chemicals are identified by empirical evidence 2. The equation must contain correct formulas e.g., KClO 3  KCl + O 2 b/c oxygen gas is O 2, not O 3 3.law of Conservation of Mass must be followed The same number of atoms of each atom must the same for reactants and products.

Diatomic Molecules: Elements that exist in pairs as gases at room temp. Br H Cl ON I F 7 – 6 = 1 = H H O N Cl Br I F

Writing Word Equations Steps in writing equations: 1.word equation 2.formula equation (unbalanced) 3.balanced chemical equation 4.net ionic equation (for precipitation reaction)

Word Equations: an equation in which the reactants and products in a chemical reaction are represented by words. Example: (photosynthesis) carbon dioxide + water  glucose + oxygen “  ” =react to yield yields produces form

Combustion reaction: hydrocarbon + oxygen  carbon dioxide + water C 6 H 12 O 6 + O 2  CO 2 + H 2 O