Section 4.3 Pg

 This often involves integrating two or more concepts.  I.e. Boyle’s and Charles’ Laws were combined to create the Combined Gas Law  Similarly, Avogadro’s Theory and the Mole concept can also be combined:  Avogadro: “Equal volumes of any gases at the same temperature and pressure contain equal numbers of entities”  Therefore, for all gases at a specific temperature and pressure, there must be a certain volume, the molar volume, that contains one mole of entities  Molar Volume: the volume that one mole of a gas occupies at a specified temperature and pressure

 Molar volume is the same for all gases at the same temperature and pressure (remember, all gases have the same physical properties)  At STP, molar volume = 22.4 L/mol ( kPa and 0°C)  At SATP, molar volume = 24.8 L/mol (100 kPa and 25°C)  This can be used as a conversion factor just like molar mass! At STP, one mole of gas has a volume of 22.4 L, which is approximately the volume of 11 “empty” 2 L pop bottles. STP = 22.4L/mol SATP = 24.8 L/mol

 Chemists created the concept of molar volume to convert between volume and chemical amount Molar Volume as a Conversion Factor V n litres mol x 1 mol x L x x L 1 mol Remember the conversion factor will be different at STP and SATP!

 Why are we dealing with molar volume instead of molar mass???  It’s a lot easier to measure the volume of a gas than trying to measure its mass.  You would have to trap the gas in a container and measure its mass on a balance and them make corrections for the buoyant force of the surrounding air... not easy

1. Calculate the volume occupied by mol of carbon dioxide at SATP. V CO 2 : mol x ( 24.8 L) = 0.60 L 1 mol 2. What chemical amount of oxygen is available for a combustion reaction in a volume of 5.6 L at STP? STP = 22.4L/mol SATP = 24.8 L/mol n O 2 : 5.6 L x ( 1 mol ) = 0.25 mol 22.4 L

3. What volume does 3.50 g of helium gas (He) occupy at SATP? n He : 3.50 g x ( 1 mol ) = mol 4.00 g V He : mol x ( 24.8 L) = 21.7 L 1 mol  Once these calculations are clearly understood, they can be combined into a single calculation using unit analysis. All units except the final unit will cancel. STP = 22.4L/mol SATP = 24.8 L/mol V He : 3.50 g x ( 1 mol ) x ( 24.8 L) = 21.7 L 4.00 g 1 mol

4. A propane tank for a barbecue contains liquefied propane. IF the tank mass drops by 9.1 kg after a month’s use, what volume of propane gas at SATP was used for cooking? Molar mass (M): C 3 H 8(g) = g/mol V C 3 H 8(g) : 9.1 kg x (1 mol ) x ( 24.8 L) = 5.1 kL 44.11g 1 mol  What if I wanted your answer in litres? STP = 22.4L/mol SATP = 24.8 L/mol 5.1 kL x 1000L = 5100 L= 5.1 x 10 3 L 1 kL

STP = 22.4L/mol SATP = 24.8 L/mol Molar volume: the volume that one mole of a gas occupies at a specified temperature and pressure Homework: pg. 171 #5 - 12