Journal #13 Determine the molecular formula of a compound with an empirical formula of NH2 and a formula mass of amu.

Chemical Reactions Chemical reaction is the process by which one or more substances are changed into one or more different substances. In any chemical reaction, the original substances are the reactants and the resulting substances are the products. A chemical equation represents, with symbols and formulas, the identities and relative molecular or molar amounts of the reactants and products in a chemical reaction

Exothermic vs Endothermic Endothermic reactions require heat for them to occur Exothermic reactions release heat in the reaction.

Indications of a chemical reaction Evolution of energy as heat and light. A change in matter that releases energy as both heat and light Production of gas Gas bubbles Formation of a precipitate A solid appears after 2 solutions are mixed Color change

Characteristics of Chemical Equations The equations must represent known facts. All reactants and products must be identified The equation must contain the correct formulas for the reactants and products. The law of conservation of mass must be satisfied Atoms can neither be created nor destroyed in ordinary chemical reactions. The same number of atoms must appear on each side of a chemical equation.

Word and Formula Equations Word equation- an equation in which the reactants and products in a chemical reaction are represented by words Formula equation- represents the reactants and products of a chemical reaction by their symbols and formulas Symbols used in chemical equations (pg 266)

Let’s Practice Write word and formula equations for the chemical reaction that occurs when solid sodium oxide is added to water at room temperature and forms sodium hydroxide (dissolved in water). Include symbols for physical states in the formula equation. Sodium oxide + water  sodium hydroxide Na2O + H2O  NaOH (not balanced) Na2O (s) + H2O (aq)  NaOH (aq)

Practice Translate the following chemical equation into a sentence BaCl2 (aq) + Na2CrO4 (aq)  BaCrO4 (s) + 2NaCl (aq) Each reactants is an ionic compound and is named according to the rules of such compounds. Both reactants are in aqueous solution. One product is a precipitate and the other remains in solution. The equation is translated as follows: Aqueous solutions of barium chloride and sodium chromate react to produce a precipitate of barium chromate plus sodium chloride in aqueous solution.