1. Stoichiometry CaCO3 a CaO + CO2
involves the mass relationships between reactants and products in a chemical reaction.
Example
CaCO3 a CaO + CO2
10 g
? g
or ? g

2. 2 H2 + O2 a 2 H2O 2 molecules 1 molecule 2 molecules 2000 molecules
2 dozen molecules
1 dozen molecules
2 dozen molecules
2 moles molecules
1 mole molecules
2 moles molecules
1 dozen = 12
1 mole = 6.02 x 1023

3. The coefficients represent the number of moles reacting (not the number of grams).
2 H O2 a 2 H2O
2 grams
? grams
2 moles
2 moles
2 grams of H2 does not make 2 grams H2O
but
2 moles of H2 does make 2 moles H2O

4. 2 2 H2 + O2 a 2 H2O 1 Stoichiometry Problem 4 moles H2 ? moles O2 2x
____________ =
2 moles O2
moles H2
molar ratio step

5. 2 H2 + O2 a 2 H2O 2 2 4 ? moles H2O 4 moles H2 moles H2O 4 moles H2 x
____________ =
4 moles H2O
moles H2
molar ratio step

6. 2 H2 + O2 a 2 H2O 2 1 6 grams H2 1.5 ? moles O2 3 moles H2 6 grams H2
1 mole H2
moles O2 x
____________ x
____________ =
1.5 moles O2
2 grams H2
moles H2
molar ratio step
3 moles H2

7. 2 H2 + O2 a 2 H2O 90 grams H2O 5 moles H2 5 moles H2O 10 grams H2
1 mole H2 2
moles H2O 18
grams H2O x x
____________ x
____________
___________ =
2 grams H2 2
moles H2 1
mole H2O
90 grams H2O
5 moles H2

8. 2 H O2 a 2 H2O
90 grams H2O
10 grams
? grams
5 moles H2
5 moles H2O

9. Change moles A to moles C
A B a C
Grams A
Moles A
Moles C
Grams C
Change grams to moles
Change moles A to moles C
Change moles to grams