Hoa dai cuong_chuong 6

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General Chemistry: Chapter 6
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Chapter 6: Gases
Philip Dutton
University of Windsor, Canada

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General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th Edition
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General Chemistry: Chapter 6
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Contents
6-1 Properties of Gases: Gas Pressure
6-2 The Simple Gas Laws
6-3 Combining the Gas Laws:
The Ideal Gas Equation and
The General Gas Equation
6-4 Applications of the Ideal Gas Equation
6-5 Gases in Chemical Reactions
6-6 Mixtures of Gases

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General Chemistry: Chapter 6
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Contents
6-6 Mixtures of Gases
6-7 Kinetic—Molecular Theory of Gases
6-8 Gas Properties Relating to the
Kinetic—Molecular Theory
6-9 Non-ideal (real) Gases
Focus on The Chemistry of Air-Bag Systems

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General Chemistry: Chapter 6
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6-1 Properties of Gases: Gas Pressure
Gas Pressure



Liquid Pressure
P = g ·h ·d
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General Chemistry: Chapter 6
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Barometric Pressure
Standard Atmospheric Pressure
1.00 atm
760 mm Hg, 760 torr
101.325 kPa
1.01325 bar
1013.25 mbar

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General Chemistry: Chapter 6
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Manometers
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General Chemistry: Chapter 6
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6-2 Simple Gas Laws
Boyle 1662
PV = constant
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General Chemistry: Chapter 6
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Example 5-6
Relating Gas Volume and Pressure – Boyle’s Law.
P1V1 = P2V2
Vtank = 644 L
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General Chemistry: Chapter 6
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Charles’s Law
Charles 1787
Gay-Lussac 1802
V  T
V = b T
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General Chemistry: Chapter 6
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STP
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
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General Chemistry: Chapter 6
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Avogadro’s Law
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.
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Formation of Water
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General Chemistry: Chapter 6
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Avogadro’s Law
V  n or V = c n
At STP
1 mol gas = 22.4 L gas
At an a fixed temperature and pressure:
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6-3 Combining the Gas Laws: The Ideal Gas Equation and the General Gas Equation
Boyle’s law V  1/P
Charles’s law V  T
Avogadro’s law V  n
PV = nRT
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General Chemistry: Chapter 6
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The Gas Constant
= 8.3145 m3 Pa mol-1 K-1
PV = nRT
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General Chemistry: Chapter 6
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The General Gas Equation
R =
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General Chemistry: Chapter 6
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6-4 Applications of the Ideal Gas Equation
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General Chemistry: Chapter 6
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Molar Mass Determination
PV = nRT
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General Chemistry: Chapter 6
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Example 6-10
Determining a Molar Mass with the Ideal Gas Equation.
Polypropylene is an important commercial chemical. It is used in the synthesis of other organic chemicals and in plastics production. A glass vessel weighs 40.1305 g when clean, dry and evacuated; it weighs 138.2410 when filled with water at 25°C (δ=0.9970 g cm-3) and 40.2959 g when filled with propylene gas at 740.3 mm Hg and 24.0°C. What is the molar mass of polypropylene?
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General Chemistry: Chapter 6
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Example 5-6
Determine Vflask:
Vflask = mH2O  dH2O = (138.2410 g – 40.1305 g)  (0.9970 g cm-3)
= 98.41 cm3 = 0.09841 L
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General Chemistry: Chapter 6
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Example 5-6
Example 5-6
Use the Gas Equation:
PV = nRT
M = 42.08 g/mol
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General Chemistry: Chapter 6
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Gas Densities
PV = nRT
and
d =
m
V
, n =
m
M
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General Chemistry: Chapter 6
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6-5 Gases in Chemical Reactions
Stoichiometric factors relate gas quantities to quantities of other reactants or products.
Ideal gas equation used to relate the amount of a gas to volume, temperature and pressure.
Law of combining volumes can be developed using the gas law.
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General Chemistry: Chapter 6
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Example 6-10
Using the Ideal gas Equation in Reaction Stoichiometry Calculations.
The decomposition of sodium azide, NaN3, at high temperatures produces N2(g). Together with the necessary devices to initiate the reaction and trap the sodium metal formed, this reaction is used in air-bag safety systems. What volume of N2(g), measured at 735 mm Hg and 26°C, is produced when 70.0 g NaN3 is decomposed.
2 NaN3(s) → 2 Na(l) + 3 N2(g)
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Example 6-10
Determine moles of N2:
Determine volume of N2:
nN2 = 70 g N3 
1 mol NaN3
65.01 g N3/mol N3

3 mol N2
2 mol NaN3
= 1.62 mol N2
= 41.1 L
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General Chemistry: Chapter 6
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6-6 Mixtures of Gases
Partial pressure
Each component of a gas mixture exerts a pressure that it would exert if it were in the container alone.
Gas laws apply to mixtures of gases.
Simplest approach is to use ntotal, but....
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General Chemistry: Chapter 6
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Dalton’s Law of Partial Pressure
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General Chemistry: Chapter 6
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Partial Pressure
Ptot = Pa + Pb +…
Va = naRT/Ptot and Vtot = Va + Vb+…
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General Chemistry: Chapter 6
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Pneumatic Trough
Ptot = Pbar = Pgas + PH2O
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General Chemistry: Chapter 6
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6-7 Kinetic Molecular Theory
Particles are point masses in constant, random, straight line motion.
Particles are separated by great distances.
Collisions are rapid and elastic.
No force between particles.
Total energy remains constant.
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General Chemistry: Chapter 6
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Pressure – Assessing Collision Forces
Translational kinetic energy,

Frequency of collisions,

Impulse or momentum transfer,

Pressure proportional to impulse times frequency
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General Chemistry: Chapter 6
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Pressure and Molecular Speed
Three dimensional systems lead to:
um is the modal speed
uav is the simple average
urms
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General Chemistry: Chapter 6
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Pressure
Assume one mole:
PV=RT so:
NAm = M:
Rearrange:
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General Chemistry: Chapter 6
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Distribution of Molecular Speeds
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General Chemistry: Chapter 6
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Determining Molecular Speed
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General Chemistry: Chapter 6
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Temperature
Modify:
PV=RT so:
Solve for ek:
Average kinetic energy is directly proportional to temperature!
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6-8 Gas Properties Relating to the
Kinetic-Molecular Theory
Diffusion
Net rate is proportional to molecular speed.
Effusion
A related phenomenon.
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Graham’s Law
Only for gases at low pressure (natural escape, not a jet).
Tiny orifice (no collisions)
Does not apply to diffusion.
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General Chemistry: Chapter 6
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6-9 Real Gases
Compressibility factor PV/nRT = 1
Deviations occur for real gases.
PV/nRT > 1 - molecular volume is significant.
PV/nRT < 1 – intermolecular forces of attraction.
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General Chemistry: Chapter 6
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Real Gases
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General Chemistry: Chapter 6
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van der Waals Equation
P +
n2a
V2
V – nb = nRT
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General Chemistry: Chapter 6
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Chapter 6 Questions
9, 13, 18, 31, 45, 49, 61, 63, 71, 82, 85, 97, 104.