Chapter11 - 11/7/2011 CHEMISTRY CHEMISTRY 1307 Chapter XI...

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11/7/2011 1 1 CHEMISTRY 1307 CHEMISTRY 1307 Chapter XI Gases and Their Properties 2 Importance of Gases Airbags fill with N 2 gas in an accident generated by the rapid decomposition of sodium azide, NaN 3 . 2 NaN 3 (s) 2 Na(s) + 3 N 2 (g) 3 Hot Air Balloons - The States of Matter
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11/7/2011 2 4 General Properties of Gases Gases are composed of a large collection of particles in constant random motion. Gases occupy containers uniformly and completely. Gases diffuse rapidly to form homogeneous mixtures. Most of the volume of a gas is empty space. 5 Properties of Gases Gas properties are characterized by the following quantities: V = volume of the gas (__) T = temperature (__) n = amount (______) P = pressure (__________) 6 Pressure Atmospheric pressure of air is measured with a device called a _____________ First developed by Evangelista Torricelli in 1643.
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11/7/2011 3 7 Pressure Hg( l ) rises up an evacuated tube until force of Hg (down) ______ the force of atmosphere (pushing up). The pressure of the atmosphere is proportional to the __________ of the column and the density of the liquid. 8 Pressure density volume ´ d V = ´ g d V A ´ ´ = P g d h = ´ ´ = height (x) We conclude the pressure is ___________ to the density and the height of a column of a given substance. since mass (m) = force P area = m g A ´ = 3 2 Volume (x ) since Area (x ) 9 Problem Mercury has a density of 13.6 g/cm 3 and water has a density of 1.00 g/cm 3 . If a column of mercury has a height of 755 mm, how high would a corresponding column of water be in feet? Solution : We begin by setting the pressures equal: P Hg = P water Since P = g d h We can write: Hg g d ´ Hg h ´ = water g d ´ water h ´
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11/7/2011 4 10 Problem Hg Hg water water d h h d ´ = = 3 g 13.6 cm 755 mm ´ 1 cm 10 mm ´ 1 in 2.54 cm ´ 1 ft 12 in ´ 3 g 1.00 cm = 33.7 ft This is why we don t use water in a barometer! barometer! Hg g d ´ Hg h ´ = water g d ´ water h ´ h water = 11 Pressure Measurement Units Unit: Conversion to atm: Atmosphere (atm) 1 760 mm Hg = 1 atm 760 torr = 1 atm 1 mm Hg = 1torr 101,325 Pa* = 1 atm 1.01325 bar** = 1 atm **bar are often written as mbar (1 mbar = 10 3 bar) *Pa (N/m 2 ) are often written as kPa (1 kPa = 10 3 Pa) 14.696 lb/in 2 = 1 atm 12 Gas laws: Boyle’s Law As the volume of the air trapped in the pump is reduced, its pressure goes up, and air is forced into the tire A bicycle pump is a good example of Boyle s law.
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11/7/2011 5 13 Boyle’s Law The pressure of a system of gas particles is ____________________ to the volume of fixed number of moles at constant temperature. Robert Boyle (1627-1691). Son of Earl of Cork, Ireland. B 1 1 2 2 1 P V P V C PV P V μ ´ = = 14 Boyle’s Law 15 Problem A sample of nitrogen gas has a pressure of 67.5 mm Hg in a 500. mL flask. What is the pressure of this gas sample when it is transferred to a 125 mL flask at the same temperature? 1 1 2 2 1 1 2 2 67.5 mm Hg 500. mL = = = 270. mm Hg 125 mL = ´ PV P V
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