Ideal Gas Law and the Molar Volume of a Gas
Basic Assumption:
Gases at STP (273 K and 1 atm, 101.3 kPa or 760 mmHg)
have a volume of 22.4 L
How many moles of Helium are in 22.4 L?
Step 1:
1 mole of gas occupies 22.4 L
So, 22.4 L of Helium (or any gas) is 1 mole of gas
0.25 moles of Oxygen gas would have what volume?
Step 1:
1 mole is 22.4 L
(0.25 moles) x
mole
L
4
.
22
= 5.6 L
12 moles of CO
2
have what volume?
Step 1:
1 mole is 22.4 L
(12 moles) x
mole
L
4
.
22
= 268.8 L
The basic equation we will be using in this unit is:
PV=nRT
P = Pressure in kPa or atm
V = in liters
n = the number of moles
R = 8.31
K
mole
L
kPa
•
•
or 0.821
K
mole
L
atm
•
•
T = in Kelvin
Alternatively we could write this equation as:
PV=(
MW
grams
)RT
With this variant we can find the number of grams of a gas if we know the
Molecular Weight
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Sample Problems:
1.
How many moles of O
2
gas would fit in a 37.0 liter vessel at 60.00°C at a
pressure of 3.50 atm?
Step 1:
Circle the variables and assign letters
How many moles of O
2
gas would fit in a 37.0 liter vessel at 60.00°C at a
pressure of 3.50 atm?
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 Spring '08
 HOFMANN,BRUCEROB
 Mole

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