## 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
 6.0221421×1023
 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
x

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