Ch 5

• Changes in state

  Physical changes
• Changes in physical state

  • Many other physical properties may also change
• States of matter

  • Gases
  • Liquids
  • Solids
• Ideal gas

  A model of the way that gas particles behave at the atomic/molecular level
• Properties of a gas that can be measured

  • Temperature
  • Volume
  • Pressure
  • Mass

  
• Gas laws

  Relationships between number of moles (n) of gas, volume (V), temperature (T), and pressure (P)
• Pressure

  Force per unit area

  
• Gas pressure

  Result of force exerted by the collision of particles with the walls of the container
• Barometer

  Measures atmospheric pressure

  
• Common units of pressure

  • Atmosphere (atm)
  • Torr
  • Pascal (Pa)

  
• Kinetic Molecular Theory of Gases

  • Gases are made up of small atoms or molecules in constant, random, and linear motion
  • Distance of separation is very large compared to the size of the individual atoms or molecules
  • All gas particles behave independently with no attractive or repulsive forces between them
  • Gas particles collide with each other and with the walls of the container without losing energy
  • Average kinetic energy of the atoms or molecules increases or decreases in proportion to absolute temperature
• Properties of Gases

  • Easily compressible
  • Expand to fill any available volume
  • Readily diffuse through each other
  • Have low density
  • Exert pressure on their containers
  • Behave most ideally at low pressure and high temperature

  
• Boyle's law

  Volume of a gas varies inversely with the pressure exerted by the gas if the temperature and number of moles are held constant

  
• Charles's law

  Volume of a gas varies directly with the absolute temperature (K) if pressure and number of moles of gas are constant

  
• Combined gas law

  Derived from a combination of Boyle's law and Charles's law, used when a sample of gas undergoes change involving volume, pressure, and temperature simultaneously
• Avogadro's law

  Equal volumes of any ideal gas contain the same number of moles if measured under the same conditions of temperature and pressure
• Molar volume

  The volume occupied by 1 mol of any gas at standard temperature and pressure (STP)
• STP

  Standard Temperature and Pressure: T = 273 K (0°C), P = 1 atm

  
• Ideal gas constant (R)

  0.0821 L·atm/mol·K
• Calculating molar volume

  PV = nRT

  Solve for V when P = 1 atm, n = 1 mol, T = 273 K
• Dalton's law of partial pressures


  A mixture of gases exerts a pressure that is the sum of the pressures that each gas would exert if it were present alone under the same conditions

  
• Total pressure of our atmosphere is equal to the sum of the pressures of N2 and O2

  
• Ideal gases vs. real gases

  Ideal gas is a useful model, but in reality there is no such thing as an ideal gas. Nonpolar gases behave more ideally than polar gases because attractive forces are present in polar gases.