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CH301 - chapter 12 notes

CH301 - chapter 12 notes - 1 CH 301 Chapter 12 12-2 Some...

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1 CH 301 Chapter 12 12-2 Some Common Properties of Gases: { The density of gases is much less than that of solids or liquids. { Gas molecules must be very far apart compared to liquids and solids. 1. Gases can be compressed into smaller volumes ; that is, their densities can be increased by applying increased pressure . 2. Gases exert pressure on their surroundings ; in turn, pressure must be exerted to confine gases. 3. Gases expand without limits , and so gas samples completely and uniformly occupy the volume of any container. 4. Gases diffuse into one another , and so samples of gas placed in the same container mix completely. Conversely, different gases in a mixture do not separate on standing. 5. The amounts and properties of gases are described in terms of temperature, pressure, the volume occupied, and the number of molecules present . For example, a sample of gas occupies a greater volume when hot than it does when cold at the same pressure, but the number of molecules does not change. 0.00503 1.59 1.70 CCl 4 0.000588 0.998 0.917 H 2 O Gas Liquid Solid Densities (g/mL)
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2 Composition of Dry Air 12-3 Pressure (force per unit area) Barometers are used to measure the pressure the atmospheric pressure (atm). { Atmospheric pressure is measured using a barometer. { A barometer can be constructed by filling a long glass tube (sealed at one end) all the way to the top with Hg. { The tube is inverted (without letting air in) into a dish of Hg. { The Hg in the tube falls until the pressure from the mass of the Hg in the tube is balanced by the pressure of the atmosphere on the mercury in the dish. { The pressure of the atmosphere is then expressed by the height of the Hg in the tube. { Definitions of standard pressure 76 cm Hg 760 mm Hg 760 torr 1 atmosphere 101.3 kPa Because mercury barometers are very common: gas pressure is often expressed in mmHg gas pressure is also expressed in torr 1 mmHg = 1 torr atmospheric pressure decreases with increasing elevation (less mass of air) At 0 o C, 1.0 atm = 760 mmHg = 760 torr The SI unit is the pascal (Pa): 1.0 atm = 1.013 x 10 5 Pa Learn these units of pressure!!! 0.00005 H 2 0.00015 CH 4 0.002 He, Ne, Kr, Xe 0.03 CO 2 0.93 Ar 20.94 O 2 78.09 N 2 % by Volume Gas
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3 Boyle’s Law : The effect of pressure on volume of gas. At constant temperature and with a constant number of moles gas: PV = k Where: P = pressure V = volume k = a constant (determined experimentally) Robert Boyle (seventeenth century) showed that the volume of a sample of gas, under constant temperature, would decrease when the pressure was increased. An inverse relationship exists between pressure and volume When the pressure and volume were multiplied, regardless of the pressure change, the product was a certain constant number (k). An experiment is conducted in the apparatus (a) to the left to determine the relationship between volume and pressure at a fixed amount of gas.
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