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Gas Stoichiometry Molar Volume of an Ideal Gas Standard Temperature & Pressure (STP) Using these with the Ideal Gas Law

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Using Stoichiometry and Gas Laws Calculate the volume of oxygen gas (O 2 ) produced at 1.00 atm and 25 o C by the incomplete decomposition of 10.5 g of potassium chlorate: 2KClO 3 2KCl + 3O 2 – To solve the problem, we use what we know about moles and the ideal gas law: 1.Convert grams of KClO 3 to moles 2.Use a mole ratio to determine moles of O 2 3.Calculate the volume of O 2 using the ideal gas law 1) 10.5 g KClO 3 x 1 mol KClO 3 = 0.0856 mol KClO 3 122.6 g KClO 3 2) 0.0856 mol KClO 3 x 3 mol O 2 = 0.128 mol O 2 2 mol KClO 3 3) Use the ideal gas law: PV = nRT P = 1.00 atmn = 0.128 mol V = ?T = 25 o C 298 K V = (0.128 x 0.08206 x 298) = 3.13 L 1.00

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STP: Standard Temperature and Pressure 1 mole of an ideal gas at 0 o C (273 K) and 1 atm has a volume of 22.4 L This volume is called the molar volume of an ideal gas. STP = the conditions of 0 o C and 1 atm V = nRT = (1.00 mol)(0.08206)(273 K) = 22.4 L P 1.0 atm 1 mol of ANY ideal gas has a volume of 22.4 L at STP: Equivalence statement: 1.000 mol = 22.4 L (STP)

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Calculating using STP A sample of nitrogen gas has a volume of 1.75L at STP. How many moles of N 2 are present? – We can take a shortcut to the ideal gas law by using the molar volume of an ideal gas at STP: 1.000 mol = 22.4 L (STP) SO… 1.75 L x 1.000 mol N 2 = 0.0781 mol N 2 22.4 L N 2

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Reactions Involving Gases at STP Quicklime (CaO) is produced by heating calcium carbonate (CaCO 3 ). Calculate the volume of CO 2 produced at STP from the decomposition of 152 g of CaCO 3 according to the reaction: CaCO 3 CaO + CO 2 Step 1: Convert the mass of CaCO 3 to moles 152 g CaCO 3 x 1 mol CaCO 3 = 1.52 mol CaCO 3 100.1 g CaCO 3 Step 2: Determine moles of CO 2 using a mole ratio 1.0 mol CaCO 3 x 1 mol CO 2 = 1.52 mol CO 2 1 mol CaCO 3 Step 3: Use the molar volume of an ideal gas at STP to determine volume of CO 2 1.52 mol CO 2 x 22.4 L CO 2 = 34.1 L CO 2 1 mol CO 2

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Gas Stoichiometry Practice Problems 1.Calcium oxide can be used to scrub carbon dioxide from air: CaO + CO 2 CaCO 3 a.What mass of CO 2 could be absorbed by 1.25 g of CaO? b.What volume would this CO 2 occupy? 2.For the reaction 4Al + 3O 2 2Al 2 O 3 What volume of oxygen gas at STP would be needed to react completely with 1.55 g of aluminum? 3.An ideal gas has a volume of 50.0 mL at 100 o C and a pressure of 690 torr. Calculate the volume of this sample of gas at STP. 4.A gaseous mixture contains 6.25 g of He and 4.97 g of Ne. What volume does the mixture occupy at STP? 5.Using the unbalanced equation: Na + Cl 2 NaCl What volume of chlorine gas, measured at STP, is necessary for the complete reaction of 4.81 g of sodium metal?

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