Chemical Reactions Balancing Chemical Equations Types of Reactions

Remember – A chemical change occurs when substances react together and form NEW products. Examples of this include: rusting Combustion Tarnishing Fermentation oxidation Acid rain reacting with calcium in rocks

Evolution of heat and light Production of a gas Formation of a precipitate A precipitate is a solid produced as a result of a chemical reaction in solution and that separates from the solution Unexpected Color change Change in energy (absorption or evolution) Formation of water Production of an odor

Chemical reaction can be written in words or as formulas. When they are written using formulas and symbol this is called a chemical equation. Chemical reactions must contain correct reactants (the beginning substances) and products (the ending substances)

Chemical equations must be BALANCED in order to follow the LAW of Conservation of Mass, which states that mass can neither be created or destroyed. Remember… what you start with has to equal with what you end with!

To balance a chemical equation you must make sure there is the same number of each type of atom on both sides of the arrow. Only change the coefficients (the number in front of the compounds or element), never change subscripts! Diatomic molecules (di=2, atomic=atoms) (always exist as 2 when they are by themselves) N 2 O 2 F 2 Cl 2 Br 2 I 2 H 2

Remember that when balancing an equation each side has to equal. (Law of Conservation of Mass). First: Write out the equation: ___N 2 + ___H 2 ___NH 3 Count how many atoms of each element are on each side. ReactantsProducts N=2N=1 H=2H=3 This equation is NOT balanced. You will now have to add coefficients to make each side balanced.

Synthesis 2 elements or simple compounds combine to form ONE product. Examples: Generic equation: A + X  AX 8 Fe + S 8  8 FeS CaO + H 2 O  Ca(OH) 2

Decomposition ONE compound is broken down into simpler parts Examples: Generic equations: AX  A + X AXY  AX +Y 2 H 2 O  2 H 2 + O 2

Single Replacement An element and a compound combine to form a new element and compound. Metals can replace other metals and hydrogen in an acid. Halogens can replace halogens. Must look at activity series to determine if the reaction will occur (it is located on your reference sheet) Generic equations: AX + B  BX + A AX + Y  AY + X 2 Na + MgSO 4  Mg + Na 2 SO 4 Cl 2 + 2NaBr  Br NaCl

Double Replacement 2 compounds produce 2 NEW compounds. These compounds are in aqueous solution so the ions switch places with each other. Must consider solubility rules to determine which product is the precipitate, if any. Generic Equation: AX + BY  AY + BX Pb(NO 3 ) KI  PbI KNO 3

Combustion Oxygen combines with a compound to produce carbon dioxide and water. This releases large amounts of energy (heat). Generic equation: C x H y + O 2  CO 2 + H 2 O