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Published byChristine Troupe Modified over 4 years ago

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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 (O2) produced at 1.00 atm and 25oC by the incomplete decomposition of 10.5 g of potassium chlorate: 2KClO3 2KCl + 3O2 To solve the problem, we use what we know about moles and the ideal gas law: Convert grams of KClO3 to moles Use a mole ratio to determine moles of O2 Calculate the volume of O2 using the ideal gas law 1) 10.5 g KClO3 x 1 mol KClO3 = mol KClO3 122.6 g KClO3 3) Use the ideal gas law: PV = nRT P = 1.00 atm n = mol V = ? T = 25oC 298 K V = (0.128 x x 298) = 3.13 L 1.00 2) mol KClO3 x 3 mol O2 = mol O2 2 mol KClO3

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**STP: Standard Temperature and Pressure**

1 mole of an ideal gas at 0oC (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 0oC and 1 atm V = nRT = (1.00 mol)( )(273 K) = 22.4 L P atm 1 mol of ANY ideal gas has a volume of 22.4 L at STP: Equivalence statement: 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 N2 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 mol N2 = mol N2 22.4 L N2

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**Reactions Involving Gases at STP**

Quicklime (CaO) is produced by heating calcium carbonate (CaCO3). Calculate the volume of CO2 produced at STP from the decomposition of 152 g of CaCO3 according to the reaction: CaCO3 CaO + CO2 Step 1: Convert the mass of CaCO3 to moles 152 g CaCO3 x 1 mol CaCO3 = 1.52 mol CaCO3 100.1 g CaCO3 Step 3: Use the molar volume of an ideal gas at STP to determine volume of CO2 1.52 mol CO2 x 22.4 L CO2 = 34.1 L CO2 1 mol CO2 Step 2: Determine moles of CO2 using a mole ratio 1.0 mol CaCO3 x 1 mol CO2 = 1.52 mol CO2 1 mol CaCO3

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**Gas Stoichiometry Practice Problems**

Calcium oxide can be used to “scrub” carbon dioxide from air: CaO + CO2 CaCO3 What mass of CO2 could be absorbed by 1.25 g of CaO? What volume would this CO2 occupy? For the reaction 4Al + 3O2 2Al2O3 What volume of oxygen gas at STP would be needed to react completely with 1.55 g of aluminum? An ideal gas has a volume of 50.0 mL at 100oC and a pressure of 690 torr. Calculate the volume of this sample of gas at STP. A gaseous mixture contains 6.25 g of He and 4.97 g of Ne. What volume does the mixture occupy at STP? Using the unbalanced equation: Na + Cl2 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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