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Molar Volume, Avogadro's Law and (a little bit about) Dalton’s Law of Partial Pressures. MOLAR VOLUME. How much space does 1 mole of gas take up?. 1 mole of ANY gas = 22.4 L at STP How many liters does 2.8 moles of Helium take up? 2.8 mol 22.4 L = 62.72 L 1 mol
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Molar Volume, Avogadro's Law and(a little bit about) Dalton’s Law of Partial Pressures
How much space does 1 mole of gas take up? • 1 mole of ANY gas = 22.4 L at STP • How many liters does 2.8 moles of Helium take up? 2.8 mol 22.4 L = 62.72 L 1 mol • How many moles are in 137.2 L ? 137.2 L 1 mol = 6.125 moles 22.4 L
How many moles in a given volume? • You have three 1 L flasks. #1 is filled with CO2. #2 is filled with H2 and #3 is filled with C2H6. Which flask has the most number of moles of gas? THEY ARE ALL THE SAME!!!
How many molecules in 0.75 L at STP? Liters Moles Molecules Molar Avogadro’s Volume! # 0.75 L 1 mol 6.02 x 1023 molecules = 2.02 x 1022 22.4 L 1 mole molecules
EQUAL volumes of gas at EQUAL temperatures and pressures have EQUAL numbers of moles/molecules
Avogadro’s Law V1 = V2 n1 n2 • You have gaseous helium in two separate containers at the same temperature and pressure. The volume of container #1 is 3.7 L and has 8.2 moles of the gas. The volume of container #2 is 19.4 L. How many moles are in container #2? 3.7 L = 19.7 L n2 = (19.7 L)(8.2 mol) 8.2 mol n2 (3.7 L) n2 = 43.7 mol
YOU TRY IT… • You have gaseous helium in two separate containers at the same temperature and pressure. The volume of container #1 is 1.8 L and has 7.6 moles of the gas. The volume of container #2 is 3.58 L. How many moles are in container #2? 1.8 L = 3.58 L n2 = (3.58 L)(7.6 mol) 7.6 mol n2 (1.8 L) n2 = 15.1 mol
PARTIAL PRESSURES The total pressure of a gas mixture depends on the total number of gas particles, not on the types of particles. P = 1.00 atm P = 1.00 atm LecturePLUS Timberlake 1 mole H2 0.5 mole O2 + 0.3 mole He + 0.2 mole Ar
DALTON’S LAW OF PARTIAL PRESSURE • In a mixture of gases, the total pressure of the mixture equals the sum of the individual gas pressures Ptotal = Pgas1 + Pgas2 + …. + Pgasn • When a gas is collected over water, you have a mixture of your sample gas as well as water vapor
YOU CAN USE MOLE RATIOS AS IF THEY WERE PARTIAL PRESSURES • A gaseous mixture contains 2 mol Ar and 4.5 mol of CO2. It has a total pressure of 6.8 atm. What is the partial pressure of Ar? ngas = Pgas ntotal Ptotal 2 mol Ar = PAr gas PAr gas = 2.09 atm (2 mol + 4.5 mol) 6.8 atm