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Molar Volume, That Contains One Mole of Entities

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Molar Volume, That Contains One Mole of Entities Section 4.3 Pg. 169‐171 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 speciic 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 speciied temperature and pressure STP = 22.4L/mol SATP = 24.8 L/mol 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 (101.325 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. Molar Volume as a Conversion Factor Chemists created the concept of molar volume to convert between volume and chemical amount x 1 mol x L V n litres mol 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 STP = 22.4L/mol SATP = 24.8 L/mol 1. Calculate the volume occupied by 0.024 mol of carbon dioxide at SATP. VCO2 : 0.024 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? nO2 : 5.6 L x ( 1 mol ) = 0.25 mol 22.4 L STP = 22.4L/mol SATP = 24.8 L/mol 3. What volume does 3.50 g of helium gas (He) occupy at SATP? nHe : 3.50 g x ( 1 mol ) = 0.875 mol 4.00 g VHe : 0.875 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 inal unit will cancel. VHe : 3.50 g x ( 1 mol ) x ( 24.8 L) = 21.7 L 4.00 g 1 mol STP = 22.4L/mol SATP = 24.8 L/mol 4. A propane tank for a barbecue contains liqueied 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): C3H8(g) = 44.11 g/mol C H V 3 8(g) : 9.1 kg x (1 mol ) x ( 24.8 L) = 5.2 kL 44.1g 1 mol What if I wanted your answer in litres? 5.2 kL x 1000L = 5200 L = 5.2 x 103 L 1 kL Molar volume: the volume that one mole of a gas occupies at a speciied temperature and pressure STP = 22.4L/mol SATP = 24.8 L/mol Homework: pg. 171 #4 ­ 12 .
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