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1 Gases Chapter 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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2 Characteristics of Gases Gases expand to fill any container. –random motion, no attraction Gases are fluids (like liquids). –no attraction Gases have very low densities. –no volume = lots of empty space

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3 Characteristics of Gases Gases can be compressed. –no volume = lots of empty space Gases undergo diffusion & effusion. –random motion

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11 of the periodical table elements are in the gas form.

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5 Units of Pressure 1 torr = 1 mmHg 1 atm = 760 mmHg = 760 torr 1 atm = 1.01325 x 10 5 Pa = 101,325 kPa Pressure = Force Area (force = mass x acceleration) Torrc elli

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6 Sea level1 atm 4 miles0.5 atm 10 miles0.2 atm

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The atmospheric pressure at the summit of Mt. McKinley (Denali) is 606 mm Hg on a certain day. What is the pressure in atmospheres?

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8 P 1/V P x V = constant P 1 x V 1 = P 2 x V 2 Boyle’s Law Constant temperature Constant amount of gas Volume is inversely proportional to pressure

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9 A sample of chlorine gas occupies a volume of 946 mL at a pressure of 726 mmHg. What is the pressure of the gas (in mmHg) if the volume is reduced at constant temperature to 154 mL? P 1 x V 1 = P 2 x V 2 P 1 = 726 mmHg V 1 = 946 mL P 2 = ? V 2 = 154 mL P 2 = P 1 x V 1 V2V2 726 mmHg x 946 mL 154 mL = = 4460 mmHg P x V = constant

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Charles’ Law Volume is proportional to temperature

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11 As T increases V increases Variation in Gas Volume with Temperature at Constant Pressure

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Gay-Lussac’s Law Temperature is proportional to pressure

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13 Variation of Gas Volume with Temperature at Constant Pressure V TV T V = constant x T V 1 /T 1 = V 2 /T 2 Charles’ & Gay-Lussac’s Law Temperature must be in Kelvin

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14 A sample of carbon monoxide gas occupies 3.20 L at 125 0 C. At what temperature will the gas occupy a volume of 1.54 L if the pressure remains constant? V 1 = 3.20 L T 1 = 398.15 K V 2 = 1.54 L T 2 = ? T 2 = V 2 x T 1 V1V1 1.54 L x 398.15 K 3.20 L = = 192 K V 1 /T 1 = V 2 /T 2 T 1 = 125 ( 0 C) + 273.15 (K) = 398.15 K

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15 Avogadro’s Law V number of moles (n) V = constant x n V 1 / n 1 = V 2 / n 2 Constant temperature Constant pressure

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The Gas Laws Boyles Law pressure -- volume –P 1/V Charles Law temperature -- volume –V T Avogadros Law moles -- volume –V n Gay Lussac Law temperature -- pressure –P T

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17 Ammonia burns in oxygen to form nitric oxide (NO) and water vapor. How many volumes of NO are obtained from one volume of ammonia at the same temperature and pressure? 4NH 3 + 5O 2 4NO + 6H 2 O 1 mole NH 3 1 mole NO At constant T and P 1 volume NH 3 1 volume NO

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18 Ideal Gas Equation Charles’ law: V T (at constant n and P) Avogadro’s law: V n (at constant P and T) Boyle’s law: P (at constant n and T) 1 V V V nT P V = constant x = R nT P P R is the gas constant PV = nRT

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19 The conditions 0 0 C and 1 atm are called standard temperature and pressure (STP). PV = nRT R = PV nT = (1 atm)(22.414L) (1 mol)(273.15 K) R = 0.082057 L atm / (mol K) For any Gas Experiments show that at STP, 1 mole of an ideal gas occupies 22.414 L.

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20 What is the volume (in milliliters) occupied by 63.7 g of HCl at STP? PV = nRT V = nRT P T = 0 0 C = 273.15 K P = 1 atm n = 63.7 g x 1 mol HCl 36.45 g HCl = 1.75 mol V = 1 atm 1.75 mol x 0.0821 x 273.15 K Latm molK V = 39.1 L = 391 ml

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21 What is the volume (in liters) occupied by 49.8 g of HCl at STP? PV = nRT V = nRT P T = 0 0 C = 273.15 K P = 1 atm n = 49.8 g x 1 mol HCl 36.45 g HCl = 1.37 mol V = 1 atm 1.37 mol x 0.0821 x 273.15 K Latm molK V = 30.7 L

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