Chapter 13Gases
13.1 PressureObjectives: 1) To learn about atmospheric pressure and
the way in which barometers work2) To learn the various units of pressure.
13.1: Pressure
• Automobile tires, basketballs, balloons, and soda bottles.
• What happens to a balloon when you place it in a freezer?– Why?
13.1 Pressure
• Evangelista Torricelli invented the – BAROMETER: device
to measure pressure
– At sea level the height of the column of mercury is 760 mm.
Pressure exerted by the atmospheric gaseson the surface of the mercury in the dishkeeps the mercury in the tube.
13.1: Pressure
Weather:
-low pressure STORMS
-high pressure nice weather
13.1: Pressure
Units of Pressure
-mm Hg= torr
Standard atmosphere (atm)1 std. atm.=1,000 atm=760.0mm Hg=760.0 torr
1 std. atm=101, 325 Pascal1.000 atm=14.69 psi
Measuring pressure
Manometer
Atmospheric pressure-h
Atmospheric pressure + h
13.1: Pressure
The height of mercury in a mercury barometer is measured to be 732 mm. Represent this pressure in atm, torr, and pascals.
The pressure of a gas is measured to be 2.79 x 105 Pa. Represent this pressure in atm, torr, and psi.
0.963 atm; 732 torr; 9.76 x 104 Pa
2.75 atm; 2.10 x 103 torr; 40.4 psi
Homework, Self-Check exercise 13.1
13.2: Pressure and Volume: Boyle’s Law
• Objectives:
1) To understand the law that relates the pressure and volume of a gas.
2) To do calculations involving this law.
Robert Boyle: Irish scientist-studied the relationshipbetween the pressure of the trapped gas and its volume
P x V=const.
PV=k
Boyle’s Law
Inverselyproportional
Figure 13.6: Illustration of Boyle’s law.
P1V1=P2V2
13.2: Pressure and Volume: Boyle’s Law
• A sample of neon gas has a pressure of
7.43 atm in a container with a volume of 45.1 L. This sample is transferred to a container with a volume of 18.4 L. What is the new pressure of the neon gas?
Assume constant temperature.
18.2 atm
13.2: Pressure and Volume: Boyle’s Law
• A steel tank of oxygen gas has a volume of 2.00L. If all of the oxygen is transferred to a new tank with a volume of 5.50 L, the pressure is measured to be 6.75 atm. What was the original pressure of the oxygen gas?
Assume constant temperature.
18.6 atm
Homework: 7-10 p. 435
13.3: Volume and Temperature: Charles’s Law
• Objectives:
1) To learn about absolute zero.
2) To learn about the law relating the volume and temperature of a sample of gas at constant moles and pressure, and to do calculations involving that law.
13.3: Volume and Temperature: Charles’s Law
• Objectives:
1) To learn about absolute zero.
2) To learn about the law relating the volume and temperature of a sample of gas at constant moles and pressure, and to do calculations involving that law.
Jacques Charles(first solo H balloonflight)-showed that thevolume of a gas(at constant pressure)increases with the temperature.
Absolute zero:point where youget 0 volume-273oC
13.3: Volume and Temperature: Charles’s Law
• Charles’s Law
V/T= constant
V1 = V2
T1 T2
13.3: Volume and Temperature: Charles’s Law
• A 2.45 L sample of nitrogen gas is collected at 273 K and heated to 325K. Calculate the volume of the nitrogen gas at 325 K.
Assume constant pressure.
2.92 L
13.3: Volume and Temperature: Charles’s Law
• A sample of methane gas is collected at 285 K and cooled to 245K. At 245 K the volume of the gas is 75.0 L. Calculate the volume of the methane gas at 285K.
Assume constant pressure.
87.2 L
13.3: Volume and Temperature: Charles’s Law
• Consider a gas with a volume of 5.65 L at 27 C and 1 atm pressure. At what temperature will this gas have a volume of 6.69 L and 1 atm pressure.
82oC (355K)
13.3: Volume and Temperature: Charles’s Law
• Consider a gas with a volume of 9.25L at 47oC and 1 atm pressure. At what temperature does this gas have a volume of 3.50 L and 1 atm pressure.
-152oC (121K)
13.4: Volume and Moles: Avogadro’s Law
• Objective:
1) To understand the law relating the volume and the number of moles of a sample of gas at constant temperature and pressure, and to do calculations involving this law.
Avogadro’s Law
V1 = V2
n1 n2
13.4: Volume and Moles: Avogadro’s Law
If 2.55 mol of helium gas occupies a volume
of 59.5 L at a particular temperature and
pressure, what volume does 7.83 mol of helium occupy under the same conditions?
183 L
13.4: Volume and Moles: Avogadro’s Law
If 4.35 g of neon gas occupies a volume of
15.0 L at a particular temperature and pressure, what volume does 2.00 g of neon gas occupy under the same conditions?
6.90 L
13.6: Dalton’s Law of Partial Pressures
Objectives: To understand the relationship between the partial and total pressures of a gas mixture, and to use this relationship in calculations.
Scuba divers: use helium and oxygen instead of air. Air contains nitrogen that dissolves in the blood as a result of high pressure. Nitrogen bubbles out and the diver gets the bends.
13.6: Dalton’s Law of Partial Pressures
John Dalton: For a mixture of gases in a container, the total pressure exerted is the sum of the partial pressures of the gases present.
Partial pressure: pressure that the gas would exert if it were alone in the container.
Dalton’s law of partial pressures:
Ptotal=P1 + P2 + P3
Ptotal=ntotal (RT/V)
The pressure doesn’t depend on the forces amongst the particles.The volume of the individual gas particlesis not important.
Figure 13.12: The production of oxygen by thermal decomposition.
13.6: Dalton’s Law of Partial Pressures
A sample of solid potassium chlorate KClO3, was heated in a test tube and decomposed according to the reaction
2KClO3(s) 2KCl(s) + 3O2
The oxygen produced was collected by displacement of water at 22oC. The resulting mixture of O2 and H2O vapor had a total pressure of 754 torr and a volume of 0.650L. Calculate the partial pressure of O2 in the gas collected and the number of moles of O2 present. The vapor pressure of water at 22oC is 21 torr.
13.6: Dalton’s Law of Partial Pressures
Ptotal=PO2 + PH2O
754=PO2 + 21
PO2= 733 torr
nO2 =PO2V 733/760=0.964 atm RTnO2= (0.964 atm)(0.650L)
(0.08206) (295)
13.6: Dalton’s Law of Partial Pressures
A 5.00 g sample of helium gas is added to a 5.00 g sample of neon in a 2.50 L container at 27oC. Calculate the partial pressure of each gas and the total pressure.
12.3 atm He; 2.44 atm Ne; 14.7 atm total
13.6: Dalton’s Law of Partial Pressures
A sample of oxygen gas is saturated with water vapor at 30.0oC. The total pressure is 753 torr and the vapor pressure of water at 30.0 C is 31.824 torr. What is the partial pressure of the oxygen gas in atm?
0.949 atmHomework: 23-30 and 33-36
13.6: Dalton’s Law of Partial Pressures
A sample of oxygen gas is saturated with water vapor at 27oC. The total pressure is 785 torr and the partial pressure of oxygen is 758.3 torr. What is the vapor pressure of water at 27oC?
26.7 torr
13.8: The Kinetic Molecular Theory of Gases
Objectives: To understand the basic postulates of the kinetic molecular theory
Postulates of KMT.
13.9: The Implications of the Kinetic Molecular Theory
Objectives: To understand the term temperature.
To learn how the kinetic molecular theory explains the gas laws.
13.9: The Implications of the Kinetic Molecular Theory
The temperature of a gas: how rapidly, its individual particles are moving.
High temperatures: move very fast.
Low temperatures: move slower.
As the gas is heated to a higher temperature, the particles move faster, hitting the walls more often.
Pressure increases with increasing temperature
13.10: Real Gases
Objectives: To describe the properties of real gases.
As real gases are compressed into smaller and smaller volumes, the particles of the gas begin to occupy a significant fraction of the available volume..
Start to attract to eachother here PV=nRT not true
13.11:Gas Stoichiometry
Objectives:
1) To understand the molar volume of an ideal gas.
2) To learn the definition of STP
3) To use these concepts and the ideal gas equation.
13.11:Gas Stoichiometry
For 1 mol of an ideal gas at 0oC (273K) and 1 atm, the volume will be.
V=nRT/P= (1.00mol)(0.08206)(273) = 22.4L
1 atm.
22.4 L is called the molar volume
Standard temperature and pressure (abbreviated STP). Contains 1 mol of an ideal gas at STP.
13.11:Gas Stoichiometry
A sample of argon gas has a volume of 3.45 L at STP. What is the mass of the argon?
6.15 g
13.11:Gas Stoichiometry
A sample of hydrogen gas occupies a volume of 15.0L at STP. What volume will this sample occupy at 22oC and 2.50 atm?
6.48 L
13.11:Gas Stoichiometry
When magnesium reacts with hydrochloric acid, hydrogen gas is produced:
Mg(s) + 2HCl MgCl2(aq) + H2(g)
Calculate the volume of hydrogen gas produced at STP by reacting 5.00 g Mg and an excess of HCl (aq)
4.61 L
13.11:Gas Stoichiometry
When subjected to an electric current, water decomposes to hydrogen and oxygen gas: 2H2O(l) 2H2(g) + O2(g)
If 25.0g of water is decomposed, what volume of oxygen gas is produced at STP?
15.5 L
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