Chapter5_Gases

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

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1 CHAPTER 5 GASES

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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.

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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.

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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 =

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8 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.
9 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 × =

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10 Charles’ Law For the same gas sample at constant P T V T V 2 2 1 1 =
11 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 =

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12 Standard Temperature and Pressure Standard temperature and pressure (STP). Standard P 1.00000 atm Standard T 273.15 K or 0.00 o C At STP, the volume of one mole of a gas is called the standard molar volume standard molar volume . The standard molar volume is 22.4 L at STP.
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Chapter5_Gases - CHAPTER 5 GASES 1 Why do we study gases...

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