Chemical Reactions

In a chemical reaction, atoms are rearranged to form new compounds. The starting substances = reactants Ending substances = products New substances are always formed, but matter is not created or destroyed!

Chemical Reactions A Sample Chemical Reaction: Sodium reacts with Dihydrogen Monoxide to form Sodium Hydroxide and Hydrogen Gas Na + H 2 O -----> NaOH + H 2

Word Equations Word Equations = represent chemical reactions. Reactants = left side Products = right side Reactant + Reactant  Product + Product iron + oxygen  iron(III) oxide

Chemical Equations Chemical Equations = another representation of a chem. rxn, using formulas. Formulas of Reactants = Left Formulas of Products = Right side Connected by an arrow Can be either skeleton or balanced

Chemical Equations Skeleton Equations = unbalanced chemical equations. ex – Rusting: Fe + O 2  Fe 2 O 3 Balanced Equations = coefficients indicate relative amounts of reactants and products Each side has the same # of each type of atom & mass is conserved. ex – Rusting: 4 Fe + 3 O 2  2 Fe 2 O 3

Writing & Balancing Chemical Equations

Types of Chemical Reactions

Classifying Chemical Reactions There are 5 types of Chemical Reactions 1.Combination (synthesis) 2.Decomposition 3.Single Replacement 4.Double Replacement 5.Combustion

Combination (Synthesis) Reactions Combination Reaction = two or more substances combine to create one new substance. A + B  AB

Decomposition Reactions Decomposition Reaction = chemical change in which a single compound breaks down into two or more substances. AB  A + B

Single Replacement Reactions Single Replacement Reaction = a chemical change in which one element replaces a second element in a compound AB + C  AC + B Usually metals replace MUST CHECK ACTIVITY SERIES

Double Replacement Reactions Double Replacement Reaction = a chemical change involving an exchange of positive ions between two compounds. AB + CD  AD + CB Will only work under 3 conditions: 1.Precipitate (solid) is formed 2.Gas is produced 3.Water is created

Combustion Reactions Combustion Reaction = a chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light Oxygen is always a reactant Water & Carbon Dioxide are always products