# Gas Stoichiometry Molar Volume of an Ideal Gas

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

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

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)

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

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

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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