1. Stoichiometry Review

2. 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 x 1023
A mole was the name given to the quantity of atoms in exactly 12 grams of carbon-12

3. 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
= g/mol

4. 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) = g/mol
2 moles H2O
18.02 g
= g H2O
1 mole

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

6. 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 STP
1 mole

7. 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

8. 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.

10. 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 NH Mole Ratio Molar Mass N 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