Unit: Chemical Reactions Day 2 - Notes 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 Balance equations using the “tally method” heat Pt

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

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

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 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

Do not separate polyatomic ions! Examples: Balance the following equation: ___Fe2(SO4)3 + ___Na3(PO4)  ___Fe(PO4) + ___Na2(SO4) 2 3 Helpful tip: Do not separate polyatomic ions! 2 2 Fe 1 2 3 (SO4) 1 3 6 3 Na 2 6 1 (PO4) 2 1 2 YES!!!! Are we balanced?

Do now: Complete “Exit Ticket” Then: Begin WS 2 (Homework)