1. How many moles of water will be produced when 8 grams of hydrogen gas react with the oxygen in the air?
Episode 801

2. Stoichiometry
Study of the quantity (mass) relationships in a chemical reaction
Based on balanced equations
2Mg + O2  2MgO
Two atoms of magnesium reaction with 1 oxygen molecule to form 2 magnesium oxide formula units or
Two moles of magnesium atoms react with 1 mole of oxygen molecules to form 2 moles of magnesium oxide formula units
Episode 801

3. The coefficients in a balance equation give the MOLE RATIO for the substances involved in the reaction.
Example problem:
When elemental aluminum reacts with elemental iodine, aluminum iodide is produced.
2 Al + 3 I2  2 AlI3
Mole ratios: ____Al: ____I2
____Al: ____AlI3
____I2: ____AlI3
If you start with 4 moles of Al, how many moles of AlI3 will be produced? 2 3 2 2 3 2
? mol AlI3 = 4 mol Al
2 mol AlI3
= 2 mol AlI3
2 mol Al
Episode 801

4. BE SURE TO BALANCE THE EQUATION FIRST!!
Problem Set 1
N2H N2O4  N H2O
BE SURE TO BALANCE THE EQUATION FIRST!!
? mol N2H4 = 2.72 mol N2H4
? mol N2 = 2.72 mol N2H4 2 3 4
2.72 mol N2H4
1 mol N2O4
= 1.36 mol N2O4
2 mol N2H4
2.72 mol N2H4
3 mol N2
= 4.08 mol N2
2 mol N2H4
Episode 801

5. (Hint: We will need to change grams of H2 to moles H2)
How many moles of water will be produced when 8 grams of hydrogen gas react with the oxygen in the air?
2 H2 + O2  2 H2O
(Hint: We will need to change grams of H2 to moles H2)
? mol H2O = 8 g H2
1 mol H2
2 mol H2O
= 4 mol H2O
2 g H2
2 mol H2
(Hint: To “make the switch” between different substances in a reaction, use the mole ratio from the balanced equation.)
Episode 801

6. Problem Set 2 6 CO2 + 6 H2O  C6H12O6 + 6 O2
In photosynthesis, carbon dioxide and water react to form glucose, C6H12O6 and oxygen gas.
6 CO2 + 6 H2O  C6H12O6 + 6 O2
If 15.6g of carbon dioxide react, how many moles of glucose will be produced?
? mol C6H12O6 = 15.6g CO2
1 mol CO2
1 mol C6H12O6
= mol C6H12O6
44g CO2
6 mol CO2
How many grams of carbon dioxide must react to form 0.25 moles of glucose?
? g CO2 = 0.25 mol C6H12O6
6 mol CO2
44g CO2
= 66g CO2
1 mol C6H12O6
1 mol CO2
Episode 801

7. Challenge Problem
When nitrogen and hydrogen react, they form ammonia gas, which has the formula NH3. If 56.0 g of nitrogen are used up in the reaction, how many grams of ammonia will be produced?
Episode 801