Chapter 13 Gases

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Chapter 13Gases

• 13.1 Pressure
• Objectives
• To learn about atmospheric pressure and the way
  in which barometers work
• To learn the various units of pressure.

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13.1 Pressure

• Automobile tires, basketballs, balloons, and soda
  bottles.
• What happens to a balloon when you place it in a
  freezer?
• Why?

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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 gases on the
surface of the mercury in the dish keeps the
mercury in the tube.
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13.1 Pressure

• Weather
• -low pressure STORMS
• -high pressure nice weather

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13.1 Pressure

• Units of Pressure
• -mm Hg torr
• Standard atmosphere (atm)
• 1 std. atm.1,000 atm760.0mm Hg760.0 torr

1 std. atm101, 325 Pascal 1.000 std. atm14.69
psi
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Measuring pressure
Atmospheric pressure-h
Manometer
Atmospheric pressure h
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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
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13.2 Pressure and Volume Boyles Law

• Objectives
• To understand the law that relates the pressure
  and volume of a gas.
• To do calculations involving this law.

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Robert Boyle Irish scientist -studied the
relationship between the pressure of the trapped
gas and its volume
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P x Vconst. PVk Boyles Law Inversely proport
ional
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Figure 13.6 Illustration of Boyles law.
P1V1P2V2
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13.2 Pressure and Volume Boyles 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
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13.2 Pressure and Volume Boyles 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
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13.3 Volume and Temperature Charless Law

• Objectives
• To learn about absolute zero.
• 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.

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13.3 Volume and Temperature Charless Law

• Objectives
• To learn about absolute zero.
• 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.

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Jacques Charles (first solo H balloon flight) -sho
wed that the volume of a gas (at constant
pressure) increases with the temperature.
Absolute zero point where you get 0 volume -273oC
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13.3 Volume and Temperature Charless Law

• Charless Law
• V/T constant
• V1 V2
• T1 T2

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13.3 Volume and Temperature Charless 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
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13.3 Volume and Temperature Charless 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
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13.3 Volume and Temperature Charless 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)
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13.3 Volume and Temperature Charless 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)
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13.4 Volume and Moles Avogadros 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.

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Avogadros Law
V1 V2 n1 n2
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13.4 Volume and Moles Avogadros 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
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13.4 Volume and Moles Avogadros 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
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13.5 The Ideal Gas Law

• Ideal Gas Law
• PVnRT
• RUniversal gas constant (proportionality
  constant)
• R 0.08206 L atm/ oK
• Based on experimental measurements.
• Most gases obey this equation at 1 atm or lower
  and 0oC or higher

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13.5 The Ideal Gas Law

• Ideal Gas Law
• When the number of moles and type of gas are a
  constant.

P1V1 P2V2 T1 T2
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13.5 The Ideal Gas Law

• A sample of neon gas has a volume of 3.45 L at
  25oC and a pressure of 565 torr. Calculate the
  number of moles of neon present in the gas sample.

0.105 mol
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13.5 The Ideal Gas Law

• A 0.250 mol sample of argon gas has a volume of
  9.00 L at a pressure of 875 mm Hg. What is the
  temperature (in oC) of the gas?

232oC
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13.5 The Ideal Gas Law

• Consider a sample of helium gas at 23oC with a
  volume of 5.60 L at a pressure of 2.45 atm. The
  pressure is changed to 8.75 atm and the gas is
  cooled to 15oC. Calculate the new volume of the
  gas using the ideal gas law equation.

1.53 L
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13.5 The Ideal Gas Law

• Consider a sample of helium gas at 28oC with a
  volume of 3.80 L at a pressure of 3.15 atm. The
  gas expands to a volume of 9.50 L and the gas is
  heated to 43oC. Calculate the new pressure of
  the gas using the ideal gas law equation.

1.32 atm
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13.6 Daltons 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.

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13.6 Daltons 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.
• Daltons law of partial pressures
• PtotalP1 P2 P3

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Ptotalntotal (RT/V)
The pressure doesnt depend on the forces
amongst the particles. The volume of the
individual gas particles is not important.
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Figure 13.12 The production of oxygen by
thermal decomposition.
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13.6 Daltons 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.

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13.6 Daltons Law of Partial Pressures

• PtotalPO2 PH2O
• 754PO2 21
• PO2 733 torr
• nO2 PO2V 733/7600.964 atm
• RT
• nO2 (0.964 atm)(0.650L)
• (0.08206) (295)

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13.6 Daltons 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
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13.6 Daltons 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 atm
Homework 23-30 and 33-36
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13.6 Daltons 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
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13.8 The Kinetic Molecular Theory of Gases

• Objectives To understand the basic postulates of
  the kinetic molecular theory

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Postulates of KMT.
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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.

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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.

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As the gas is heated to a higher temperature, the
particles move faster, hitting the walls more
often.Pressure increases with increasing
temperature
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13.10 Real Gases

• Objectives To describe the properties of real
  gases.

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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 each other here PVnRT not
true
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13.11Gas Stoichiometry

• Objectives
• To understand the molar volume of an ideal gas.
• To learn the definition of STP
• To use these concepts and the ideal gas equation.

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13.11Gas Stoichiometry

• For 1 mol of an ideal gas at 0oC (273K) and 1
  atm, the volume will be.
• VnRT/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.

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13.11Gas 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
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13.11Gas 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
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13.11Gas 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
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13.11Gas 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