Unit: Chemical Reactions Balancing chemical equations Upper left: Thermite reaction, Fe2O3 + Al => 2Fe +2Al2O3 + HEAT!!! http://en.wikipedia.org/wiki/Thermite Upper right: potassium in water, K + H2O => KOH + H2 + HEAT Bottom right: potassium chlorate and sugar, C12H22O11 + 8KClO3 => 12CO2 + 11H2O + 8KCl + HEAT!!! http://lecturedemos.chem.umass.edu/chemReactions5_5.html Bottom left: magnesium reacting with oxygen, Mg + O2 => MgO

After today you will be able to… Explain the Law of Conservation of Atoms Differentiate between endothermic and exothermic reactions Balance equations using the “tally method” heat Pt

Chemical Reaction: When substances undergo chemical changes to form new substances.

Chemical Energy: The energy released when a chemical compound reacts to produce new compounds.

Exothermic Reaction: A chemical reaction in which heat is released to the surroundings.

Endothermic Reaction: A chemical reaction that requires heat, or pulls heat from the surroundings.

Law of Conservation of Atoms: There must be the same number of each type of atom before the reaction as after the reaction.

Coefficients: Numbers that go in front of each substance to indicate the number of atoms or molecules that are reacting or being produced.

Subscripts: Numbers that go after a substance to indicate the number of atoms or molecules immediately before the subscript.

Reactants: What is being “mixed” together in a reaction and are located on the left side of the equation

Products: What is produced from the chemical reaction and are located on the right side of the equation

Balancing Rule #1: Balance all METALS first

Balancing Rule #2: Balance all NONMETALS second

Balancing Rule #3: Balance all CARBON third

Balancing Rule #4: Balance all HYDROGEN fourth

Balancing Rule #5: Balance all OXYGEN last

Balancing Rule Add-on: Any time you have a polyatomic ion that is the same on both sides of the equation, balance it as one “thing”

Let’s try some examples!  We will be using the “tally method” to balance equations in this class.

If the numbers match on either side… You’re balanced! Examples: Balance the following equation: ___ Al + ___S  ___Al2S3 Products Reactants 2 3 2 1 Al 2 3 1 S 3 If the numbers match on either side… You’re balanced!

___ Li + ___O2  ___Li2O Examples: Balance the following equation: 4 2 1 Li 2 4 2 O 1 2

___Fe2(SO4)3 + ___Na3(PO4)  ___Fe(PO4) + ___Na2(SO4)

___C2H6 + ___O2  ___CO2 + ___H2O