1. The Ideal Gas Law
Chapter 11
Section 3

2. Standard Molar Volume of a Gas
Assume the gas is an ideal gas.
Standard molar volume of a gas: the volume occupied by one mole of a gas at STP, the value is 22.4 L
Therfore, if you know the volume of gas at STP, you can find the number of moles by using conversion factor mole
22.4 L

3. Continued
Knowing the mol of the gas at STP, you can find the volume of the gas L
1 mole
At STP, what is the volume of 7.08 mol of nitrogen gas?
159 L N2

4. Another Problem
A sample of hydrogen gas occupies L at STP. How many moles of the gas are present?
0.629 mol H2

5. PV = nRT The Ideal Gas Law
Ideal gas law: the mathematical relationship among pressure, volume, temperature, and the number of moles of a gas behaving ideally.
PV = nRT
“R” is a constant (.0821 L*atm/mol*K)
“n” is the number of moles of gas in sample

6. The Ideal Gas Constant The constant “R” is the ideal gas constant
The value and units of “R” vary according to the units used for P and V
If P is in kPa, and V is in L, then R = 8.314
Temperature has to be K

8. Problem
A tank of hydrogen gas has a volume of L and holds 14.0 mol of the gas at 12°C. What is the pressure of the gas in kPa?
Given:
V = 22.9 L
n = 14.0 mol
T = = 285 K
R = L*kPa/mol*K
P = ?

9. Solution
PV = nRT
P =
P = 1450 kPa

10. Another Relationship
You can use the ideal gas law to find the molar mass of a substance. Remember that molar mass = grams/mole.
M = molar mass
m = mass of the substance
R, T, P, and V stand for
the same quantities.

11. Problem
What is the molar mass of a gas which has a mass of g and a volume of 8.13 L at 20.0 °C and 99.2 kPa?
= 61.1 g/mol

12. Problems
Calculate the volume that a mol sample of a gas will occupy at 265 K and a pressure of 91.2 kPa.
7.80 L
What is the pressure in kPa of a mol sample of helium gas at a temperature of 20.0°C if its volume is L?
521 kPa

13. Another Problem
Determine the kelvin temperature required for mol of gas to fill a balloon to 1.20 L under kPa
307 K