Stoichiometry Review

What is a mole? Definitions: A mole (mol) is a unit used for measuring atoms, molecules, or other particles A mole is equal to the number 6.022 x 1023 A mole was the name given to the quantity of atoms in exactly 12 grams of carbon-12

Molar Mass The molar mass of an element or compound is the mass of exactly one mole of that element or compound Units are grams per mole (g/mol) To find molar mass, add up the masses from the periodic table for the compound Ex: H2O = H + H + O H = 1.01 O = 16.00 1.01 + 1.01 + 16.00 = 18.02 g/mol

Converting between Grams and Moles To convert between grams and moles, use the molar mass as a conversions factor (molar mass) grams = 1 mole Ex: How many grams in 2 moles of water? Molar mass of water (H2O) = 18.02 g/mol 2 moles H2O 18.02 g = 36.04 g H2O 1 mole

Converting between Atoms/Molecules and Moles Use Avogadro’s number as a conversion factor 1 mole = 6.022 x 1023 atoms/molecules/particles Ex: How many moles in 1.2044 x 1024 molecules of H2O? 1.2044 x 1024 molecules H2O 1 mole = 2 moles H2O 6.022 x 1023 molecules

Converting between Liters of a gas and Moles Use the volume of a gas at STP 1 mole of a gas at STP = 22.4 L Ex: How many liters would 3 moles of He occupy at STP? 3 moles He 22.4 L = 67.2 L He @ STP 1 mole

Converting between Moles of two different compounds or elements This only applies when we have a chemical equation to work with! To convert, use the mole ratio as your conversion factor Ex: For the equation 2 H2 + O2  2 H2O, if I have 3.4 moles of H2, how many moles of O2 do I need? Mole Ratio (from coefficients) 1 mol O2 : 2 mol H2 3.4 moles H2 1 mole O2 = 1.7 moles O2 2 mole H2

Mole Island The following chart can help you remember how to convert between units as well as how to string together multi-step conversions! Just find your starting and ending points, then do each conversion you cross along the path.

Converting from grams of one element/compound to grams of another Follow the mole island path! Example: N2 + 3 H2  2 NH3 For the above reaction, how many grams of nitrogen gas would I need to make 10 g of NH3? Grams of NH3  moles of NH3  moles of N2  grams of N2 Start Molar Mass NH3 Mole Ratio Molar Mass N2 Answer 10 g NH3 1 mole NH3 1 mole N2 28.02 g N2 = 8.22 g N2 17.04 g NH3 2 mole NH3