The Mole-Volume RelationshipObjective1. Identify the volume of a quantity of a gas at STP.

Mole-Volume Relationship• Look at 1 mol of table sugar, 1 mol of table salt. Notice

that the volumes of one mole of different solid substances are different.

• Molar volumes of different liquids are also different.

• How about molar volumes of gases?

Avogadro’s Hypothesis• In 1881 Avogadro first proposed the following idea:

Equal volumes of gases at the same temperature and pressure contain equal number of particles.

• The reverse of Avogadro’s hypothesis is that equal number of gas particles at the same temperature and pressure have the same volume.

• In each container, the volume occupied by the gas molecules is extremely small compared to the volume of its container.

• Therefore the volume of gas particles are negligible.

• Whether the gas particles are large or small, they occupy the same volume at same temperature and pressure.

Volume of a Gas

Gas Volume and Temperature• How does temperature affect the volume of a gas?

Volume of a gas varies with a change in temperature

• When temperature increases, volume increases. When temperature decreases, volume decreases.

Gas Volume and Pressure• How does pressure affect the volume of a gas?

Volume of a gas varies with a change in pressure

• When pressure increases, volume decreases.

• When pressure decreases, volume increases.

Standard Temperature and Pressure

• Because the volume of a gas varies with temperature and pressure, the volume of a gas usually measured at a Standard Temperature and Pressure (STP).

• STP means 00 C and a pressure of 101.3 kPa or 1 atm

Molar Volume of a Gas

• At STP, one mol of any gas occupies volume of 22.4 L

• At STP 6.02 x 1023

representative particles of a gas occupies 22.4 L.

• The quantity, 22.4 L is called molar volume of a gas.

Gas

• Unlike solids and liquids, the molar volume of gases is predictable, but is affected by temperature and pressure

• What unit is used for the mass of a mole?• What unit is used for the volume of a mole?

Molar Volume of a Gas

• Molar volume of a gas is 22.4 L/mol

1 L H2 1 L CH4 1 L N2

• Is the volume of these gases equal? • Is the number of molecules of these gases equal? • Are the masses of these gases equal?• Is the number of moles of these gases equal?

All three gases are at STP

Assessment: Gas Volume

Mole –Volume Relationship

Practice Problems1. What is the volume of these gases at STP?

a. 3.20 x 10-3 mol CO2

b. 3.70 mol N2

2. At STP, what volume do these gases occupy?a. 1.25 mol Heb. 0.335 mol C2H6

c. 1.34 mol SO2

3. How many moles of nitrogen gas will be contained in a 2.00L flask at STP?

1. (a) 7.17 x 10-2 L CO2 (b) 82.9 L N2

2. (a) 28.0 L He (b) 7.50 L C2H6 (c) 30.0 L SO2

3. 0.09 mol

Practice Problems4. What volume will 0.416 g of krypton gas occupy at STP?5. What volume in milliliters will 0.00922 g of H2 gas occupy

at STP?6. How many grams of carbon dioxide gas are in a 1.0 L

balloon at STP?

Practice Problems4. What volume will 0.416 g of krypton gas occupy at STP?5. What volume in milliliters will 0.00922 g of H2 gas occupy

at STP?6. How many grams of carbon dioxide gas are in a 1.0 L

balloon at STP?

(4) 0.111 L (5) 102 mL (6)2.0 g

Practice Problems7. A gas has density of 0.902 g/L at STP. What is the

molar mass of this gas?8. What is the density of oxygen gas at STP?9. Sulfur dioxide has a density of 3.58 g/L at STP. What is

the molar mass of this gas?10. What is the density of krypton gas at STP?

7. 20.2 g/mol 8. 1.43 g/L 9. 80.2 g/mol 10. 3.74 g/L

The Mole Road Map