Avogadro’s
Principle and Ideal
Gas Law
Unit 6
Mar. 16, 2015
AVOGADRO’S PRINCIPLE
A. Avogadro’s Principle
 Equal
volumes of gases
contain equal numbers of
moles
• at constant temp & pressure
• true for any gas
V
k
n
V
n
Avogadro’s Principle
 From
Avogadro’s principle:
• One mole (6.02 x 1023 particles)
of any gas at STP (standard
temperature and pressure)
occupies a volume of 22.4 L.
• This is called the Molar volume
of a gas
Molar Volume
 Gases
are measured in liters
 Under certain conditions……
1 mole of any gas = 22.4L
 These
conditions are known as
STP….
• Pressure = 1 atm
• Temperature = 273K
Mole Conversions
 If
we are given the # of Moles of
a gas, we can determine its
volume in Liters, at STP.
 REMEMBER…
• 1M of gas = 22.4L
V
V = M x 22.4L
M = V ÷ 22.4L
M
22.4L
Example:
Converting Between Moles & Liters of Gas
Question: How many moles are in
65.7 L of sodium?
V
M
22.4L/M
Solution: Moles = Volume ÷ 22.4L/M
Moles = 65.7 L ÷ 22.4 L/M
Moles = 2.93 M
Problem 1
 Calculate
the volume
that .881 mole of a gas
at STP will occupy.
V
M
22.4L/M
Problem 2
• What is the volume of
7.17 g of neon gas at
STP?
V
M
22.4L/M
Problem 2
• What is the volume of 7.17 g
of neon gas at STP?
V
M
22.4L/M
GAS STOICHIOMETRY
STOICHIOMETRY
The Stoichiometry Flow Chart
•LIKE A MASS TO MASS PROBLEM
•CONVERT TO MOLES
•MOLE RATIO
•CONVERT TO LITERS/GRAMS
EXAMPLE # 1
2 H2 (g) + O2 (g)  2 H2O (g)
How many moles of H2 are necessary to react
with 2 liters of O2 in order to produce water?
Step: Convert liters to moles (÷ by 22.4 L)
Step: Mole Ratio to get moles of Hydrogen
Molar Volume Stoichiometry Problems
What volume of H2, measured at STP, can be
released by 42.7 g of zinc as it reacts with
HCl?
Zn (s) + 2 HCl (aq) → H2 (g) + ZnCl2 (aq)
Step 2: Convert grams to moles (÷ by MM of Zn)
Step 3: Mole Ratio to get moles of Hydrogen
Step 4: Convert moles of H2 into liters (x by 22.4 L)