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Chapter5_Gases

Chapter5_Gases - 1 CHAPTER 5 GASES 2 Why do we study gases...

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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 well-being. 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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Chapter5_Gases - 1 CHAPTER 5 GASES 2 Why do we study gases...

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