Chapter 5. Gases

Chapter 5. Gases - Chapter 5. Gases Chem. 1A van Koppen...

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Chapter 5. Gases Chem. 1A van Koppen Consider the three physical states of substances: solid, liquid and gas. Gases occupy the full volume of their containers. Gases are generally highly compressible. When a gas is subjected to pressure, its volume decreases. Gases form homogeneous mixtures with other gases. Chemical properties vary significantly for gases. Physical properties are simpler to understand. The most useful physical properties for describing gases are: volume, V, pressure, P, and temperature, T. By studying these properties, we can understand the behavior of gases. Pressure is the force acting on an object per unit area: P = F/A Gravity exerts a force on the earth's atmosphere. Atmospheric pressure is measured using a barometer. If a tube, completely filled with mercury (Hg), is inverted into a dish of mercury, mercury will flow out of the tube until the pressure of the column of mercury equals the pressure of the atmosphere on the surface of the mercury in the dish. The height of the mercury in the tube is 760 mm for 1 atm of pressure. Units : 1 atm = 760 mm Hg = 760 torr = 14.69 psi = 1.013251 x 10 5 Pa atm = standard atmosphere, psi = pounds per square inch, Pa = pascal = 1 kg m -1 sec -2 Gas Laws: Boyle's Law: V α (1/P) (fixed temperature and fixed amount of gas) The volume of a fixed quantity of gas at a fixed temperature is inversely proportional to pressure, that is, an decrease in pressure causes the volume to increase. Charles' Law : V α T (fixed pressure and fixed amount of gas) The volume of a fixed quantity of gas at constant pressure increases as the temperature increases. A plot of V versus T is a straight line and the intercept of this plot, when T is measured in o C, is – 273.15 o C. The absolute zero of temperature is defined as 0 K = – 273.15 o C. T(in Kelvin) = T(in o C) + 273.15 Avogadro's Law : V α n (fixed pressure and fixed temperature) For a gas at constant temperature and pressure the
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This note was uploaded on 04/24/2011 for the course CHEM 1A taught by Professor Van koppen during the Fall '07 term at UCSB.

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Chapter 5. Gases - Chapter 5. Gases Chem. 1A van Koppen...

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