# A.P. Chemistry Chapter 5 Gases.

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A.P. Chemistry Chapter 5 Gases

Pressure Units (p. 189) Velocity = Acceleration = Force = Pressure = Pascal (Pa) = 1 N/m2 1 torr = 1 mm Hg 1 atm = 760 mm Hg 1 atm = 101,325 Pa = x 105 Pa = x 102 kPa

Barometer- (p. 188) used to measure atmospheric pressure; actual value is affected by location, temperature, and weather conditions. Invented by Evangelista Torricelli (unit torr is named in his honor) Manometer- (p. 189) used to measure the pressure of gases other than the atmosphere Problem: The pressure exerted by a gas is measured to be atm. Convert this pressure to torr and to Pascals.

Figure 5.2 A Torricellian Barometer

Figure 5.3 A Simple Manometer

Temperature Units: Lord Kelvin identified -273
Temperature Units: Lord Kelvin identified oC as absolute, theoretically the lowest attainable temperature. The Kelvin temperature scale uses absolute zero as the starting point; one Kelvin is equal in magnitude to one degree Celsius. Boyle’s Law: (p ) the pressure of a fixed amount of gas at a constant temperature is inversely proportional to the volume of the gas. (Pressure-Volume Relationship) P 1/V (k1 is a constant) P = k1 x 1/V PV = k1 P1V1 = k1 = P2V2 P1V1 = P2V2 Problem: A gas that has a pressure of 1.3 atm occupies a volume of 27 L. What volume will the gas occupy if the pressure is increased to 3.9 atm at constant temperature?

Charles’s Law: (p )the volume of a fixed amount of gas maintained at constant pressure is directly proportional to the absolute temperature of the gas. (Volume-Temperature Relationship) V T V = k2T (k2 is a constant) V/T = k2 V1/T1 = k2 = V2/T2 V1/T1 = V2/T2 Problem: A gas at 30.0oC and 1.00 atm occupies a volume of L. What volume will the gas occupy at 60.0oC and 1.00 atm?

Gay-Lussac’s Law: (p. 45)the pressure of a fixed amount of gas at constant volume is directly proportional to the absolute temperature of the gas. (Pressure- Temperature Relationship) P T P = k3T (k3 is a constant) P/T = k3 P1/T1 = k3 = P2/T2 P1/T1 = P2/T2

Avogadro’s Law: (p ) at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of the gas present. (Volume- Amount Relationship) V n V = k4n (k4 is a constant) V1/n1 = k4 = V2/n2 V1/n1 = V2/n2 Problem: A 5.20 L sample at 18.0oC and 2.00 atm pressure contains moles of a gas. If we add an additional 1.27 moles of the gas at the same temperature and pressure, what will be the total volume occupied by the gas?

Combined Gas Law: P1V1 = n1RT1 P2V2 = n2RT2
If n1 = n2, then Problem:A sample of methane gas (CH4) at atm and 4.0oC occupies a volume of 7.0 L. What volume will the gas occupy if the pressure is increased to 1.52 atm and the temperature is increased to 11.0oC?

Ideal Gas Law: (p )An ideal gas is a hypothetical gas whose pressure-volume-temperature behavior is completely accounted for by the ideal gas equation. The molecules of an ideal gas do not attract or repel one another, and their volume is negligible compared with the volume of the container. (There is no such thing as an ideal gas, but this law approximates gas behavior at most temperature and pressure ranges.) PV = nRT Where R is the gas constant. R = L atm/mol K = N m/K mol = J/K mol (see Units for the Gas Constant) Problem #1: A sample containing moles of a gas at 12.0oC occupies a volume of 12.9 L. What pressure does the gas exert?

Problem #2: How many moles of a gas at 104oC would occupy a volume of 6.8 L at a pressure of 270 mm Hg? Problem #3: What volume will 1.18 moles of O2 occupy at STP?