1. Ch. 11: Molecular Composition of Gases
11.1 Volume-Mass Relationships of Gases

2. Gay-Lussac’s Law of Combining Volumes of Gases
at constant T and P, coefficients in balanced equation represent ratio of volumes of gaseous reactants too
2H2(g) + O2(g)  2H2O(g)
2 L 1 L 2 L

3. Example
3O2(g)  2O3(g)
How many liters of O3 can be made from 12 L of O2?
How many moles of O2 are needed to make 24 moles of O3?
How many molecules of O3 can be made from 18 molecules of O2?

4. Avogadro’s Law
equal volumes of gases at the same T and P contain equal numbers of molecules
at same T and P, volumes varies directly with number of moles (n)
V = kn

5. Molar Volume of Gases like molar mass but with volume
mass of one mole of substance
but with volume
volume of one mole of substance
because of Avogadro’s law, one mole of any gas has the same volume as any other gas at the same T and P

6. Molar Volume of Gases Standard Molar Volume of Gas
volume of one mole of gas at 1 atm and 0°C is 22.4L
22.4 L of any gas has one mole of particles but has different masses
Standard Temperature and Pressure
STP
1 atm and 0°C

7. Molar Volume of Gases

8. Example
A chemical reaction produces mol of oxygen gas. What volume in liters is occupied by this gas sample at STP?
1 mol : 22.4 L

9. Example 2
A chemical reaction produced 98.0 mL of sulfur dioxide gas at STP. What was the mass of gas made?
convert mL to L
convert L to moles using molar volume
convert moles to grams using molar mass

10. Example 3
A chemical reaction produced 3.1 g of CO2 gas. What volume will it have in mL at STP?
convert grams to moles
convert moles to liters
convert liters to milliliters

11. Example 4
How many moles of gas are in a container with a volume of 2.46 L at STP?