1. Energy and Reactions Breaking of bonds requires an input of energy. The formation of bonds requires a release of energy. The total energy that exists before the reaction is the same as the amount of energy after the reaction. Energy in a chemical reaction can change form. Energy is never created or destroyed.

2. Conservation of Mass

3. Energy and Reactions Endothermic reaction: a chemical reaction that requires an input of energy. The amount of energy that is needed to break bonds in the reactants is greater than the amount of energy that is released as the bonds form in the products. Exothermic reaction: a chemical reaction in which energy is released. The amount of energy that is released as the products form is greater than the amount of energy that is absorbed to break bonds in the reactants.

4. Parts of a Chemical Equation Reactant: a substance that takes part in a chemical reaction. Product: the substance that is formed from a chemical reaction. A + BC + D

5. Describing Chemical Reactions Word Equation Methane and oxygen yield carbon dioxide and water Unbalanced Equation CH 4 + O 2  CO 2 + H 2 O Balanced equation CH 4 + 2O 2  CO 2 + 2H 2 O

6. Coefficient: The number in front of a compound. Balancing Chemical Equations Unbalanced equation CH 4 + O 2  CO 2 + H 2 O 22 Balanced equation

7. 7 Balanced chemical reactions follow the Law of Conservation of Mass. The number of atoms of each element on the left side of the equation is the same as on the right side. Fe + O 2  Fe 2 O 3 Let’s work with the following equation: Balancing Chemical Equations

8. 1.Write the element symbol and the number of atoms for the reactants and the products. 2.Use Trial and Error to determine how many of each molecule are a part of the reaction. Fe + O 2  Fe 2 O 3 Fe = O = 2 2 3 4

9. Balancing Chemical Equations __KClO 3 __KCl + __O 2 __NaBr + __CaF 2 __NaF + __CaBr 2 __ P + __O 2 __P 2 O 5 2 23 22 2524