Chapter Six

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Chapter Six

• Gases, Liquids and Solids

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States of Matter

• Attractive forces are broken by increasing energy
• Solid gt Liquid gt Gases
• Intermolecular Forces
• Solids high gases low
• Compressibility
• Liquids hydraulics
• Gases SCUBA

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Gases

• Measurement of Pressure
• Definition pressure force per unit area
• Units
• mmHg torr
• atm atmospheres 1 atm 760 mmHg 760 torr
• 29.92 in. Hg 1 atm

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Other Measurements

• Temperature kelvins
• K C 273
• Volume liters
• 1 liter 1000 mL
• moles n

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Gas Laws

• Boyles Law
• As pressure increases, volume decreases
• P x V constant
• P1V1 P2V2 P3V3

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Gas Laws

• Charles Law
• As temperature increases, volume increases
• V/T constant
• V1/T1 V2/T2 V3/T3

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Gas Laws

• Gay-Lussacs Law
• As temperature increases, pressure increases
• P/T constant
• P1/T1 P2/T2 P3/T3

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Combined Gas Law

• P1V1T2 P2V2T1

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Examples

• The volume of a gas at 18ºC is 960 liters. If
  the pressure is constant, what is the temperature
  if the volume is increased to 1200 L?
• answer 91ºC

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• 2. A gas has a pressure of 0.95 atm at 25ºC. If
  the volume is constant, what is the new pressure
  as the temperature is increased to 125ºC ?
• answer 1.27 atm

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• 3. What is the pressure in a 10.0 cc syringe as
  the plunger is pushed from 10.0 cc to 2.00 cc?
  (atmospheric pressure is 14.7 psi)
• answer 73.5 psi

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• 4. A gas occupies 3.50 L at 22.0ºC and 1.14 atm.
  What is the volume at 30.0ºC and 1.20 atm?
• answer 3.42 liters

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Gas Laws

• Avogadros Law
• As the number of moles increases, volume
  increases
• V/n constant
• V1/n1 V2/n2 V3/n3

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Universal Gas Law(Ideal Gas Law)

• PV nRT
• R 0.0821 liter x atm/K x mol
• R 62.4 liter x torr/K x mol

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Standard Molar Volume

• STP standard temperature and pressure
• P 1 atm 760 mmHg 760 torr
• T 0ºC 273 kelvins
• Volume of one mole of any gas at STP
• 22.4 liters

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Density of Gases at STP

• MW/22.4 density (g/L) at STP
• air 80 N2 1.25 g/L
• CH4 (natural gas) 0.71 g/L (floats in air)
• C3H8 (LP gas) 1.96 g/L (sinks in air)

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Examples

• How many moles of gas will occupy 0.55 L at 347K
  and 2.5 atm?
• answer 0.0483 mol

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• 2. Which has more molecules
• 2.0 L of CO2 at 300K and 500 mmHg
• 1.5 L of N2 at 57ºC and 1 atm
• answer N2

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• Which one weighs more?
• answer CO2

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Intermolecular Forces

• Hold molecules to each other
• (Not covalent or ionic)
• Three types

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London Forces

• vander Waals or Induced Dipole
• All molecules
• Short-lived

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• Increase with increasing molecular weight

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• Increase with more spread out molecules
• 2,2-dimethylpropane, bp 9.5ºC
• pentane, bp 35ºC

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Dipole-Dipole Forces

• Polar molecules permanent dipole
• Positive and negative ends attract
• Butane, MW58.0 g/mol, bp -0.5ºC
• Acetone, MW58.0 g/mol, bp 56.2ºC

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Hydrogen Bonding

• Hydrogen bonded to highly electronegative element
• Fluorine, Oxygen and Nitrogen (FON)
• Structures of Ammonia and Water
• Boiling points

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Density of Water

• 1.00 g/mL at 4C
• Decreases as temperature increases or decreases
• Ice is less dense than water

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Vapor Pressure and Boiling Point

• Vapor Pressure

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• Boiling point is the temperature at which the
  vapor pressure is equal to atmospheric pressure.
• Normal boiling point is the temperature at which
  the vapor pressure is equal to 760 mm Hg

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• Boiling Point
• Intermolecular Forces
• Molecular Shape

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Solids

• Crystalline solids
• Amorphous solids
• See display case behind SB168

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Phase Changes

• Heat of Fusion amount of heat energy (cal)
  required to change a substance from the solid to
  the liquid form
• Heat of Vaporization - amount of heat energy
  (cal) required to change a substance from the
  liquid to the gas form