1
Reaction Stoichiometry
–quantitative relationships between reactants and
products
4.1 Mole-to-Mole Calculations
•Stoichiometric relations in chemical equations
2H2+ O2→→ 2H2O
2 mol H2⇔⇔ 1 mol O2
1 mol O2⇔⇔ 2 mol H2O
•Conversion method
–mole ratios (conversion factors)
[2 mol H2O/1 mol O2]
(mol given)××(mole ratio)= (mol required)
Example: Determine the number of moles of
water produced from 3.4 mol O2.
OH mol 8.6
O mol 1
OH mol 2
O mol 3.4 2
2
2
2=
×
•
Stoichiometric conversion factors are reaction
specific
Example: Calculate the amount of O2needed
to produce 3.5 mol H2O by combustion of
methane (CH4).
⇒balanced equation:
CH4+ 2O2→→ CO2+ 2H2O
⇒mole ratio (conversion factor):
2 mol O2⇔⇔ 2 mol H2O
[2 mol O2/2 mol H2O]
2
2
2
2O mol 5.3
OH mol 2
O mol 2
OH mol 3.5 =
×
4.2 Mass-to-Mass Calculations
•Conversion method
Fig. 4.4
Example:
•Calculate the mass of oxygen needed to
completely burn 5.4 kg of butane (C4H10).
⇒balanced equation:
2C4H10 + 13O2→→ 8CO2+ 10H2O
⇒mole ratio (conversion factor):
13 mol O2⇔⇔ 2 mol C4H10
[13 mol O2/2 mol C4H10]
⇒molar masses:
C4H10 →→ 58.1 g/mol O2→→ 32.0 g/mol
