stoichiometry - used to find quantitative information about the substances in reactions  

• based on law of conservation of mass (discovered by Antoine Lavoisier)
• atoms are neither created/destroyed in chemical reactions
• atoms are only rearranged

chemical equations - represents chemical reactions  

• reactants >> products
• reaction must have same number of each atom on both sides to be balanced
  • balanced equation - Cl2 + O >> Cl2O
  • unbalanced equation - H2 + O2 >> H2O
• use only coefficients to balance the equation (don't change subscripts)
• best to always balance the elements that appear in the fewest formulas on each side

combination reaction - 2+ substances react to form 1 product  

• metal/nonmetal combine to form ionic solids
• A + B >> C
  • C + O2 >> CO2
  • CaO + H2O >> Ca(OH)2

decomposition reaction - 1 substance reacts to produce 2+ substances  

• usually involves heating
• C >> A + B
  • CaCO3 >> CaO + CO2
  • 2KClO3 >> 2KCl + 3O2

combustion reaction - rapid reactions that produce a flame  

• usually involves O
• usually forms water and carbon dioxide when hydrocarbons are burned
  • C3H8 + 5O2 >> 3CO2 + 4H2O
  • 2CH3OH + 3O2 >> 2CO2 + 4H2O

formula weight - sum of the atomic weights in each chemical formula  

• equal to atomic weight if finding the weight of an element
• aka molecular weight if finding the weight of a compound
• formula units - represents the chemical formulas of substances; useful to describe ionic compounds (formula unit of ionic compounds same as its empirical formula)
• percent composition - percentage of mass of each element in a substance; equal to number of atoms times atomic weight divided by formula weight
• Find the percent composition of carbon in C2H2 (acetylene)
  • 2(12) / (2 x 12 + 2 x 1) = 24 / 26 = 0.92 = 92%
• Find the percent composition of oxygen in C6H8O6 (ascorbic acid)
  • 6(16) / (6 x 12 + 8 x 1 + 6 x 16) = 96 / 176 = 0.55 = 55%