Chemistry 121

Rules for balancing equations:

1. NEVER change subscripts

2. Place coefficient in front of the formula

3. There should be an equal number of a chemical’s molecules on each side of the equation

Combination Reaction
two or more substances react to form one product
Ionic solid
Substance produced when a combination reaction occurs between a metal and a nonmetal
Decomposition reaction
one substance undergoes a reaction to produce two or more other substances
Combustion reactions

  • rapid reactions that produce a flame
  • usually involve O2 as a reactant
  • when hydrocarbons react with oxygen, the products formed are CO2 and H2O

Oxidation reactions
similar to combustion reactions, but take place in a series of steps
Formula weight
the sum of the atomic weights of each atom in its chemical formula
Molecular weight
formula weight of a molecule
Percentage composition of a compound
the percentage by mass contributed by each element in the substance
Formula for the percent of an element

% element = (# of atoms in element) (atomic weight of element) ;100

formula weight of compund

Mole (mol)

  • common unit for dealing with the number of atoms, ions, or molecules in a common sized sample
  • the amount of matter that contains as many objects as 12g of isotopically pure carbon (6.0221421;1023)
  • 1 mol samples of different substances will have different masses
  • The mass of a single atom of an element (in amu) is numerically equal to the mass (in grams) of 1 mol of that element

Avogadro’s number
Molar mass

  • mass in grams of one mole of a substance (mass in g/mol)
  • molar mass of a substance is always numerically equal to formula weight (in amu)

Mole ratios in relation to empirical formulas
the ratio of the number of moles of each element in a compound gives the subscripts in a compound’s emipirical formula
Coefficients in a balanced chemical equation
indicate both the relative number of molecules (or formula units) in the reaction AND the relative number of moles
Formula for percent yield

Percent yield =; ; actual yield;;;; ;100%

;;;;;;;;;;; theoretical yield

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