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Unformatted text preview: 1 CHAPTER 5 GASES 2 Why do we study gases? Many gaseous substances are essential to our survival and wellbeing. The behaviors of gases are relatively simple at molecular level. It provides the basis to study more complicated states, such as liquids and solids. 3 Comparison of Solids, Liquids, and Gases The density of gases is much less than that of solids or liquids. Densities (g/mL) Solid Liquid Gas H 2 O 0.917 0.998 0.000588 CCl 4 1.70 1.59 0.00503 Gas molecules must be very far apart compared to liquids and solids. 4 Properties of Gases Variables to describe a gas sample: P V T n 5 Pressure and Temperature at Molecular Level Pressure is related to the frequency of collision of gas molecules with the surface. Temperature is related to the average speed of gas molecules. 6 Pressure Pressure is force per unit area. lb/in 2 (psi) N/m 2 (pascal) mmHg or torr atm Standard pressure 760 mm Hg 760 torr 1 atm 1.01325x10 5 Pa Hg density = 13.6 g/mL 7 Boyle’s Law • the inverse relationship between volume and pressure when temperature and the amount of gas remain constant. • V ∝ 1/P constant PV 8 Boyle’s Law P in Increase surface with molecules gas of collision frequent More decreased, is V if T, constant At 9 Boyle’s Law For the same sample of gas at constant T , P 1 V 1 = P 2 V 2 Use your intuition to decide if the volume will go up or down when the pressure is changed. 10 Charles’ Law The volume of a gas is directly proportional to its absolute temperature at constant pressure and amount of gas.. Kelvin scale must be used. K = C + 273.15 Absolute zero: 273.15 C V ∝ T or T constant V 11 Charles’ Law V in increase surface with molecules gas of collision more molecules gas of speed average faster increased, is T if P, constant At 12 Charles’ Law For the same gas sample at constant P T V T V 2 2 1 1 13 Avogadro’s Law The volume of gas at a given temperature and pressure is directly proportional to the number of moles (or # of molecules) of gas. V ∝ n or n V n V 2 2 1 1 14 Standard Temperature and Pressure Standard temperature and pressure (STP)....
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 Summer '08
 ZHAO
 Chemistry, Mole

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