March 16, 2016
Avogadro's Law
-equal moles of gas (at the same temperature & pressure)
occupy equal volumes
OR
-equal volumes of gas (at the same temperature & pressure)
contain equal moles
OR
-volume and moles are directly proportional
(if T and P are constant)
n1 = n2
V1 V2
Example:
25.0 g of nitrogen gas occupies a volume of 30.0 L in a flexible
container. If 15.0 grams of nitrogen is added to the container with no
change in temperature or pressure, what will be the new volume of
the container?
March 16, 2016
Law of Combining Volumes (an application of Avogadro's Law)
The mole ratio of reacting gases can be determined from the ratio of
volumes that react
For instance
hydrogen + oxygen -----> water
10 mL
5 mL
10 mL
The law of combining volumes can be used to predict volumes of
reacting gases from a balanced equation.
Example: the combustion of octane (C8H18)
What volume of oxygen is required to completely react with 100 mL
of octane vapour in an engine cylinder?
March 16, 2016
What volume of oxygen gas would react with 35.0 mL of
hydrogen gas at STP, according to the equation
2 H2 (g) + O2 (g) ----> 2 H2O (g)
Molar Volume of a Gas:
-the volume occupied by one mole of a gas at a particular
temperature and pressure
-gases are unique because the equal moles of a gas will have the
same volume at the same T and P (no matter what the gas is)
-this relationship is not true for liquids or solids
Example: 3.00 grams of helium gas has a volume of 19.5 L at 80 kPa
and 20 ˚C. What is the molar volume of helium at this temperature
and pressure?
March 16, 2016
2 Molar Volumes to Remember
STP
22.4 L/mol
SATP
24.8 L/mol
A sample of nitrogen gas has a volume of 65.0L at SATP.
What mass of hydrogen gas is in the sample?
March 16, 2016