05 Gases - AP Chemistry GASES THE PROPERTIES OF GASES Only 4 quantities are needed to define the state of a gas a the quantity of the gas n(in moles b

05 Gases - AP Chemistry GASES THE PROPERTIES OF GASES Only...

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AP* Chemistry GASES *AP is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product. © 2008 by René McCormick. All rights reserved. Early barometer THE PROPERTIES OF GASES Only 4 quantities are needed to define the state of a gas : a) the quantity of the gas, n (in moles) b) the temperature of the gas, T ( in KELVINS) c) the volume of the gas, V (in liters) d) the pressure of the gas, P (in atmospheres) A gas uniformly fills any container, is easily compressed & mixes completely with any other gas. GAS PRESSURE : A measure of the force that a gas exerts on its container. Force is the physical quantity that interferes with inertia. Gravity is the force responsible for weight. Force = mass × acceleration; Newton’s 2 nd Law. The units of force follow: N = kg × m/s 2 Pressure -- Force/ unit area; N/m 2 Barometer --invented by Evangelista Torricelli in 1643; uses the height of a column of mercury to measure gas pressure (especially atmospheric) 1 mm of Hg = 1 torr 760.00 mm Hg = 760.00 torr =1.00 atm = 101.325 kPa 10 5 Pa At sea level all of the above define STANDARD PRESSURE. The SI unit of pressure is the Pascal (Blaise Pascal); 1 Pa = 1 N / m 2 The manometer —a device for measuring the pressure of a gas in a container. The pressure of the gas is given by h [the difference in mercury levels] in units of torr (equivalent to mm Hg). a) Gas pressure = atmospheric pressure – h b) Gas pressure = atmospheric pressure + h Exercise 1 Pressure Conversions The pressure of a gas is measured as 49 torr. Represent this pressure in both atmospheres and pascals. 6.4 × 10 -2 atm 6.5 × 10 3 Pa
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