Stoichiometry and the Math
of Equations
Part 2: Mass-Volume
Objectives
• -Determine the molar relationships
between reactants and products in a
reaction equation
• -Use molar relationships and molar
volume to convert between mass and
volumes of components in a reaction
2
Equations
• Equations are quantitative-there is a
mathematical relationship between
reactants and products
a) mass-mass problems
b) mass-volume problems
c) volume-mass problems
d) volume-volume problems
•
3
Molar Volume
• Molar volume- the volume of 1 mole of ANY
gas
– Directly related to the number of gas
molecules
– 1 mole of any gas contains the same
number of molecules (6.02  1023) so the
volume of 1 mole of any gas is the same
volume! 22.4 liters!
4
Molar Volume
• The volume of one mole is affected by
temperature and pressure changes
– Assume we’re working under standard
conditions of temp and pressure, called
STP, which is T =273 K (0° Celsius) and P
=1 atm pressure
•
Conversion factors:
22.4 liters OR 1 mole
1 mol
22.4 liters
5
Molar Volume Problem #1
• Mass – Volume
• How many liters of hydrogen will combine
with 10.0 grams of oxygen to make water
vapor?
• Steps
(1) write and balance the equation
(2) indicate the given and required
(3) indicate the mole relationship between
the given and the required below the
equation
6
How many liters of hydrogen will combine
with 10.0 grams of oxygen to make water
vapor?
• Steps (1-3)
?L
10.0 g
2 H2
+
O2  2 H2O
2 mole
1 mole
? L H2 =
• Step (4)
10.0 g O2 x 1 mol O2 x 2 mol H2 x 22.4 L H2
1
32.0 g O2
1 mol O2 1 mol H2
= 14.0 L H2
7
Molar Volume Problem #2
• Volume – Mass
• How many grams of hydrogen will combine
with 15 liters of oxygen to make water
vapor?
• Steps (1-3)
?g
2 H2
2 mole
15 L
+
O2

2 H2O
1 mole
8
How many grams of hydrogen will combine
with 15 liters of oxygen to make water
vapor?
• Step (4)
?gH=
15L O2 x 1 mol O2 x 2 mol H2 x 2.02g H2 =
1
22.4 L O2 1 mol O2
1 mol H2
= 2.7 g H2
9
Molar Volume Problem #3
• Volume-Volume
How many liters of water vapor can be
made if 5.0 liters of hydrogen
combine with oxygen?
Steps (1-3)
5.0L
2 H2
+
2 mole
O2

?L
2 H2O
2 mole
10
How many liters of water vapor can be made
if 5.0 liters of hydrogen combine with
oxygen?
• Step (4)
? L H2O =
5.0 L H2 x 1 mol H2 x 2 mol H2O x 22.4 L H2O
1
22.4 L H2 2 mol H2
1 mol H2O
= 5.0 L H2O
11
Objectives
• -Determine the molar relationships
between reactants and products in a
reaction equation
• -Use molar relationships and molar
volume to convert between mass and
volumes of components in a reaction
12