Gases, Liquids, and Solids

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Chapter 7

• Gases, Liquids, and Solids

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Sec 7.1 Kinetic and Potential Energy

• Kinetic energy is the energy that matter has
  due to particle motion
• Potential energy is the energy that matter has
  due to position, condition, and composition
• Also thought of as stored energy

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Sec 7.2 Physical States

• Solids, liquids, and gases can be understood by
  the balance of kinetic and potential energy
• The forces of potential energy are cohesive and
  want to keep the matter together, while the
  forces of kinetic energy are disruptive and want
  to break the matter apart

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Sec 7.2 Physical States

• Solids are the physical state characterized by
  the dominance of potential energy over kinetic
  energy
• Liquids are the state characterized by the
  balance of PE and KE
• Gases are the state characterized by the
  dominance of KE over PE

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Sec 7.2 Physical States

• Properties of gases due to the dominance of KE
  over PE
• Indefinite volume and indefinite shape
• Low density
• Large compressibility (subject to changes in
  pressure)
• Moderate thermal expansion (the volume is tied to
  the temperature)

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Sec 7.3 Gas Law Variables

• The behavior of gases (this is much easier than
  for solids or liquids) is able to be described by
  mathematical laws
• These Gas Laws describe the relationships between
  Pressure (P), Temperature (T), Volume (V), and
  the amount of gas (n)

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Sec 7.3 Gas Law Variables

• Units
• Kelvin Scale (K)
• Liters or mL
• Moles
• Several unit types
• 1 atm760 torr760mm Hg

• Variable Type
• Temperature (T)
• Volume (V)
• amount of gas (n)
• Pressure (P) New

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Sec 7.4 Boyles Law (P and V)

• Boyles Law states
• The volume of a fixed amount of gas is
  inversely proportional to the pressure, if
  temperature is kept constant
• For this law T is constant, n is constant. Only
  P and V will change
• P1 X V1 P2 X V2

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Sec 7.4 Boyles Law (P and V)

• Figure 7.8
• Consider a syringe
• Figure 7.9
• Both demonstrate
• Boyles Law

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Sec 7.4 Boyles Law (P and V)

• Boyles Law (P1 X V1 P2 X V2) examples
• At constant temperature, a sample of 6.0L N2 at
  2.0 atm is allowed to expand until the volume
  reaches 9.5L. What is the new pressure?
• A sample of H2 occupies 2.25L at a pressure of
  628 mm Hg, what will the volume be if the
  pressure is decreased to 428 mm Hg?

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Sec 7.5 Charless Law (T and V)

• Charless Law states
• The volume of a fixed amount of gas is directly
  proportional to the temperature, if pressure is
  kept constant
• For this law P is constant, n is constant. Only
  T and V will change
• V1 V2
• T1 T2

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Sec 7.5 Charless Law (T and V)

• Charless Law example
• A sample of dry air with a volume of 125mL at a
  temperature of 35 oC is heated at constant
  pressure to 95 oC. What will the new volume be in
  milliliters?

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Sec 7.6 Combined Gas Law

• Note that Boyles Law only applies at constant T
• Note that Charless Law only applies at constant
  P
• However, both laws can be combined and thus any
  of the quantities can be variable
• P1 V1 P2 V2
• T1 T2

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Sec 7.6 Combined Gas Law

• Combined gas law example
• A sample of O2 gas occupies a volume of 1.62L
  at 755 mm Hg pressure and a temperature of 0
  oC. What volume in L, will the gas occupy at 725
  mm Hg and 50 oC
• Solve for the missing variable, then plug in.

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Sec 7.7 The Ideal Gas Law

• The previous three laws (Boyle, Charles,
  Combined) all involve changing the gas variables
  from state 1 to state 2
• The ideal gas law only deals with 1 state, but
  allows us to bring in the 4th variable, the
  amount of gas (n)
• The ideal gas law says that for one state
• PV nRT

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Sec 7.7 The Ideal Gas Law

• PV nRT
• P is pressure, V is volume, T is temperature (in
  Kelvin), n is the amount of gas (in moles) and R
  is the gas constant
• R is simply a constant that depends on the units
  chosen for the variables of P and V
• Know this formula

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Sec 7.8 Daltons Law

• Any sample of gas exerts a pressure on the
  container around it
• Daltons Law says that for a mixture of gases,
  the pressure of the mixture is simply the total
  added pressure of each of the gases individually
• In other words Ptotal Pgas 1 Pgas 2

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Sec 7.8 Daltons Law

• Figure 7.14 Page 159
• Illustrating Daltons Law of Partial Pressure

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Sec 7.9 Changes of State

• A change of state is a process by which matter
  transforms from one physical state to another
• There are terms to describe the change from any
  state to another (six in total)
• We often overlook the fact that under rare
  conditions, a solid can transition directly to a
  gas and vice versa

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Sec 7.9 Changes of State

• Dry ice
• sublimes

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Sec 7.9 Changes of State

• Figure 7.15
• page 161

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Sec 7.9 Changes of State

• Changes of state usually occur due to changes in
  temperature and pressure
• There are two main types, endothermic and
  exothermic
• Endothermic meaning heat is absorbed
• Melting, sublimation, and evaporation
• Exothermic meaning heat is released
• Freezing, deposition, and condensation

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Sec 7.9 Changes of State
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Sec 7.9 Changes of State
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Problems

• Assigned problems pages 172 - 175
• 7.5, 7.7, 7.9, 7.10
• 7.11, 7.12, 7.13, 7.15, 7.17, 7.18
• 7.29, 7.31, 7.32, 7.33, 7.34
• Practice Test Page 175