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# Exam1reviewanswers - 1 A sample of CO2 with a pressure of...

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1. A sample of CO 2 with a pressure of 76.0 mm Hg in a volume of 0.200 L is compressed so that the new pressure of the gas is 90.0 mm Hg. What is the new volume of the gas? Assume that temperature is constant. a. P 1 = 76.0 mm Hg; V 1 = 0.200 L ; P 2 = 90.0 mm Hg ; V 2 = ??? b. P 1 V 1 = P 2 V 2 c. V 2 = P 1 V 1 / P 2 d. V 2 = [(76 mm Hg)(.200 L)] / (90 mm Hg) = . 169 L 2. Suppose you have a sample of CO 2 in a gas-tight syringe. The gas volume is 38.0 mL at 25˚C. What is the final volume of the gas if you hold the syringe in your hand to raise its temperature to 40˚C? a. V 1 = 38 mL ; T 1 = 25˚C ; T 2 = 40˚C ; V 2 = ???? b. T 1 = 25 + 273 = 298 K c. T 2 = 40 + 273 = 313 K d. V 1 / T 1 = V 2 / T 2 e. V 2 = T 2 x (V 1 / T 1 ) f. V 2 = (313 K) x (38 mL / 298 K) = 40 mL 3. You have a 34.0 L cylinder of helium at a pressure of 110 atm and a temperature of 43˚C. How many balloons can you fill, each with a volume of 26.0 L, on a day when the atmospheric pressure is 600 mm Hg and the temperature is 15˚C? a. V 1 = 34 L ; P 1 = 110 atm ; T 1 = 43˚C ; P 2 = 600 mm Hg ; T 2 = 15˚C ; V 2 = ??? b. P 2 = 600 mm Hg x 1 atm / 760 mm Hg = .7895 atm c. T 1 = 43 + 273 = 316 K d. T 2 = 15 + 273 = 288 K e. General Gas Law P 1 V 1 / T 1 = P 2 V 2 / T 2 f. V 2 = (P 1 V 1 T 2 ) / (T 1 P 2 ) g. V 2 = (110 atm x 34 L x 288 K) / (316 K x .7895 atm) = 4317.57 L h. Volume of a balloon is 26L i. 4317.57 / 26 = 166.06 j. The number of balloons that can be filled are 166. 4. A hot air balloon is filled with 2000 grams of H 2 . If the temperature of the gas is 32˚C and its pressure is 800 mm Hg, what is the volume of the balloon? a. 2000 grams H 2 x 1 mol / 1.0079 g = 1984.3238 mol H 2 b. 32 + 273 = 305 K c. 800 mm Hg x 1 atm / 760 mm Hg = 1.053 atm d. PV = nRT e. V = nRT / P f. V = [(1984.3238 mol H 2 )(.08206 (L∙atm)/(mol∙K))(305 K)] / (1.053 atm) g. V = 47181 L ≈47200 L 5. A .306 gram sample of a gaseous compound has a pressure of 400 mm Hg in a volume of 225 mL at 27˚C. What is its molar mass? a. Mass = .306 gram ; P = 400 mm Hg ; V = 225 mL ; T = 27˚C

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b. Density of the gas = grams / Liter i. V = 225 mL x 1 L / 1000 mL = .225 L ii. d = .306 grams / .225 L = 1.36 g / L c. M = dRT / P i. 400 mm Hg x 1 atm / 760 mm Hg = .52634 atm ii. [(1.36 g / L)(.08206 (L∙atm)/(mol∙K))(300 K)] / (.52632 atm) iii. M = 63.6 grams / mole 6. You choose to make some deuterium gas, D 2 , for use in an experiment and one way to make is to react heavy water, D 2 O, with the active metal lithium.
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