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6-1 6-2 6-3 Properties of Gases: Gas Pressure The Simple Gas Laws Combining the Gas Laws: The Ideal Gas Equation and The General Gas Equation Applications of the Ideal Gas Equation Gases in Chemical Reactions Mixtures of Gases Kinetic— Molecular Theory of Gases Gas Properties Relating to the Kinetic— Molecular Theory Nonideal (Real) Gases
CHM 25 SP07 LU Chapter 6: Gases
CHM 25 Spring 2007 Dr. Berk & Dr. Koel
Slide 1 of 23 CHM 25 SP07 LU 6-4 6-5 6-6 6-7 6-8 6-9 Slide 2 of 23 Importance of Gases
Airbags fill with N2 gas in an accident. Gas is generated by the decomposition of sodium azide, NaN3. General Properties of Gases
There is a lot of “ ” free space in a gas. Gases can be expanded infinitely. Gases occupy containers uniformly and completely. Gases diffuse and mix rapidly.
Slide 4 of 23 CHM 25 SP07 LU 2 NaN3 ---> 2 Na + 3 N2
Slide 3 of 23 CHM 25 SP07 LU Properties of Gases: Gas Pressure The gaseous states of three halogens. Properties of Gases
Gas properties can be modeled using math. Model depends on— Most common gases are colorless H2, O2, N2, CO and CO2
Slide 5 of 23 CHM 25 SP07 LU Slide 6 of 23 V = volume of the gas (L) T = temperature (K) n = amount (moles) P = pressure (atmospheres)
CHM 25 SP07 LU CHM 25 SP07 LU 1 The Concept of Pressure The pressure exerted by a solid. Both cylinders have the same mass They have different areas of contact P (Pa) =
Slide 7 of 23 Liquid Pressure
The pressure exerted by a liquid depends on: The height of the column of liquid. The density of the column of liquid. Force (N) Area (m2)
CHM 25 SP07 LU P = g ·h ·d
CHM 25 SP07 LU Slide 8 of 23 Pressure
Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643) Pressure
Hg rises in tube until force of Hg (down) balances the force of atmosphere (pushing up). P of Hg pushing down related to Hg density column height
CHM 25 SP07 LU Slide 10 of 23 CHM 25 SP07 LU Slide 9 of 23 Pressure
Column height measures P of atmosphere 1 standard atm = 760 mm Hg = 760 torr = 29.9 inches Hg = about 34 feet of water SI unit is PASCAL, Pa, where 1 atm = 101.325 kPa
Slide 11 of 23 CHM 25 SP07 LU Simple Gas Laws
P 1 V PV = constant Slide 12 of 23 CHM 25 SP07 LU CHM 25 SP07 LU 2 Boyle’ Law s
A bicycle pump is a good example of Boyle’ s law. As the volume of the air trapped in the pump is reduced, its pressure goes up, and air is forced into the tire. Charles’ Law s
Charles’ original balloon s Gay-Lussac 1802 VT V=bT
Modern long-distance balloon Slide 13 of 23 CHM 25 SP07 LU Slide 14 of 23 CHM 25 SP07 LU Charles’ Law s The volume of a fixed amount of gas at constant pressure is directly proportional to the Kelvin (absolute) temperature. Charles’ Law s Balloons immersed in liquid N2 (at -196 ˚C) will shrink as the air cools (and is liquefied).
Slide 15 of 23 CHM 25 SP07 LU Slide 16 of 23 CHM 25 SP07 LU Standard Temperature and Pressure Gas properties depend on conditions. Define standard conditions of temperature and pressure (STP). P = 1 atm = 760 mm Hg T = 0°C = 273.15 K
Slide 17 of 23 CHM 25 SP07 LU Avogadro’ Law s
Gay-Lussac 1808 Small volumes of gases react in the ratio of small whole numbers. Avogadro 1811 Equal volumes of gases have equal numbers of molecules and Gas molecules may break up when they react.
Slide 18 of 23 CHM 25 SP07 LU CHM 25 SP07 LU 3 Avogadro’ Hypothesis s
Equal volumes of gases at the same T and P have the same number of molecules. Formation of Water Vn or V=cn V and n are directly related. twice as many molecules
Slide 19 of 23 CHM 25 SP07 LU Slide 20 of 23 CHM 25 SP07 LU Combining the Gas Laws V proportional to 1/P V prop. to T V prop. to n Therefore, V prop. to nT/P V = 22.4 L for 1.00 mol when Combining the Gas Laws: The Ideal Gas Equation and the General Gas Equation Boyle’ law s Charles’ law s V 1/P VT V Standard pressure and temperature (STP) At STP T = 273 K P = 1.00 atm 1 mol gas = 22.4 L gas
Slide 21 of 23 CHM 25 SP07 LU Avogadro’ law V n s nT P PV = nRT
Slide 22 of 23 CHM 25 SP07 LU The Gas Constant PV = nRT
R= PV nT = 0.082057 L atm mol-1 K-1 = 8.3145 m3 Pa mol-1 K-1 = 8.3145 J mol-1 K-1
Slide 23 of 23 CHM 25 SP07 LU CHM 25 SP07 LU 4 ...
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