Chapter 11 Outline - Chemistry 101 Vandan Desai Chapter 11:...

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Chemistry 101 Vandan Desai P a g e | 1 Chapter 11: Properties of Gases (Lecture Outline) --------------------------------------------------------------------------------------------------------------------------- I. Familiar properties of gases can be explained at the molecular level A. All substances have three phases—solid , liquid , and gas B. Liquid/solid substances under ordinary conditions may also exist as gases (vapors ) C. Gas molecules only occupy a small fraction of volume of their containers i. In other words, the density of gas is low ii. As a result, each molecule of gas behaves largely as though other molecules were absent D. Different gases have different properties (i.e., toxicity, odor, color, etc.) E. Many of the properties of gases differ from those of solids and liquids : i. Gases are highly compressible ii. Gases fill the volume of their containers iii. Gases exert pressure iv. Gas pressure is dependent on the amount in the container v. When a gas is subjected to pressure , its volume decreases vi. Gases always form homogeneous mixtures with other gases vii. Gas pressure increases with temperature II. Pressure is a measured property of gases A. Pressure force acting on an object per unit area ( Pressure = Force / Area ) i. SI units of pressure are pascals (Pa) ii. 1 Pa = 1 #/m 2 iii. 1 # = 1 kg•m/s 2 iv. 1 bar = 10 5 Pa B. Pressure on Earth i. Gravity exerts a force on the Earth’s atmosphere ii. Collisions involving molecules in the air create atmospheric pressure iii. The average pressure at sea level is 1 atmosphere (1 atm) It equals the pressure required to support a column of mercury that is 760 mm high at 0°C 1 atm = 760 mm Hg = 101,325 Pa (exactly) C. Important non-SI units i. Standard atmospheric pressure is the pressure required to support 760 mm of Hg in a column Atmospheres (atm) Millimeter of mercury ( mm Hg ) or Torr ii. 1 atm = 760 mm Hg = 760 torr = 101.325 kPa (need to know these) iii. 1 atm = 14.70 lb/in 2 = 1.01325 x 10 5 Pa iv. 1 bar = 10 5 Pa D. Atmospheric Pressure and the Barometer i. Pressure of a gas comes from the molecules colliding with container walls Depends on the number of molecules , temperature
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Chapter 11 Outline - Chemistry 101 Vandan Desai Chapter 11:...

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