1. Stoichiometry

2. What is stoichiometry?
stoichiometry- method of determining the amounts of reactants needed to create a certain amount of products.
we will combine balancing equations with molar mass and add one more step.

3. How to do it
the coefficients in a balanced equation are ratios of the molecules needed for the reaction.
moles are just a number of molecules
so 2 H2 + O2  2 H2O
How many moles of H2O are made by completely reacting 1.4 mol of O2
1.4 mol O2
2 mol H2O
1 mol O2
=2.8 mol H2O

4. Adding in molar mass
How many grams of H2 are needed to completely react with 24 g of O2?
2 H2 + O2  2 H2O
convert to moles  convert to the desired molecule  convert to grams
O2 = g/mol ; H2 = g/mol
24 g O2
1 mol O2
2 mol H2
2.016 g H2
32 g O2
1 mol H2
= 3.0 g H2

5. Practice How many grams of H2O are produced from 15 g of H2?
2 H2 + O2  2 H2O
15 g H2
1 mol H2
2 mol H2O
g H2O
2.016 g H2
2 mol H2
1 mol H2O
= 130 g H2O

6. practice
How many grams of H2O are produced by completely reacting 24 g of O2?
2 H2 + O2  2 H2O
convert to moles  convert to the desired molecule  convert to grams
O2 = g/mol ; H2O = g/mol
24 g O2
1 mol O2
2 mol H2O
g H2O
32 g O2
1 mol H2O
= 27 g
H2O

7. Another How many grams of H2 are needed to form 34 g of H2O?
2 H2 + O2  2 H2O
convert to moles  convert to the desired molecule  convert to grams
H2 = g/mol ; H2O = g/mol
34 g H2O
1 mol H2O
2 mol H2
2.016 g H2
g H2O
2 mol H2O
1 mol H2
= 3.8 g H2

8. Balance the equation 1st, then do the problem
Na + Cl2  NaCl
How many grams of chlorine are needed to react with 37 g of Na? 2 2
37 g Na
1 mol Na
1 mol Cl2
70.90 g Cl2
22.99 g Na
2 mol Na
=57 g Cl2

9. More
CH4 + O2  H2O + CO2
How many grams of CH4 are needed to make 120 g of H2O? 2 2
120 g H2O
1 mol H2O
1 mol CH4
g CH4
g H2O
2 mol H2O
= 53 g CH4