Chemistry chapter 10

• Characteristics of Gases


  • Composed mainly of nonmetallic elements with simple formulas and low molar masses
  • Expand to fill their containers
  • Are highly compressible
  • Have extremely low densities
  • Two or more gases form a homogeneous mixture
• Properties Which Define the State of a Gas Sample

  • Temperature
  • Pressure
  • Volume
  • Amount of gas, usually expressed as number of moles
• Pressure


  The amount of force applied to an area
• Units of Pressure


  • Pascals
  • Bar
  • mm Hg or torr
  • Atmosphere
• Manometer


  Used to measure the difference in pressure between atmospheric pressure and that of a gas in a vessel
• Standard Pressure


  Normal atmospheric pressure at sea level, equal to 1.00 atm, 760 torr (760 mmHg), 101.325 kPa
• Boyle's Law


  The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure
• Mathematical Relationships of Boyle's Law

  • PV = a constant
  • If we compare two conditions: P1V1 = P2V2
  • A graph of V vs 1/P will result in a linear relationship
• Charles's Law


  The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature
• Mathematical Relationships of Charles's Law

  • V = constant * T
  • If we compare two conditions: V1/T1 = V2/T2
  • A graph of V vs T will be linear
• Avogadro's Law


  1. The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas

  2. At STP, one mole of gas occupies 22.4 L
• Mathematical Relationships of Avogadro's Law

  • V = constant * n
  • If we compare two conditions: V1/n1 = V2/n2
• Ideal-Gas Equation


  PV = nRT
• Density of Gases


  d = MP/RT
• Density & Molar Mass of a Gas

  • d = MP/RT
  • M = mRT/PV
• Volume and Chemical Reactions

  Use PV = nRT to relate volume, moles, and other variables
• Dalton's Law of Partial Pressures


  The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone
• Mole Fraction


  The ratio of moles of a substance to total moles in a mixture
• Pressure and Mole Fraction

  The partial pressure of a gas is proportional to its mole fraction
• Characteristics of Gases


  • Composed mainly of nonmetallic elements with simple formulas and low molar masses
  • Expand to fill their containers
  • Are highly compressible
  • Have extremely low densities
  • Two or more gases form a homogeneous mixture
• Properties Which Define the State of a Gas Sample

  • Temperature
  • Pressure
  • Volume
  • Amount of gas, usually expressed as number of moles
• Pressure


  The amount of force applied to an area
• Units of Pressure


  • Pascals
  • Bar
  • mm Hg or torr
  • Atmosphere
• Manometer


  Used to measure the difference in pressure between atmospheric pressure and that of a gas in a vessel
• Standard Pressure


  Normal atmospheric pressure at sea level, equal to 1.00 atm, 760 torr (760 mmHg), 101.325 kPa
• Boyle's Law


  The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure
• Mathematical Relationships of Boyle's Law

  • PV = a constant
  • If we compare two conditions: P1V1 = P2V2
  • A graph of V vs 1/P will result in a linear relationship
• Charles's Law


  The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature
• Mathematical Relationships of Charles's Law

  • V = constant * T
  • If we compare two conditions: V1/T1 = V2/T2
  • A graph of V vs T will be linear
• Avogadro's Law


  1. The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas

  2. At STP, one mole of gas occupies 22.4 L
• Mathematical Relationships of Avogadro's Law

  • V = constant * n
  • If we compare two conditions: V1/n1 = V2/n2
• Ideal-Gas Equation


  PV = nRT
• Density of Gases


  d = MP/RT
• Density & Molar Mass of a Gas

  • d = MP/RT
  • M = mRT/PV
• Volume and Chemical Reactions

  Use PV = nRT to relate volume, moles, and other variables
• Dalton's Law of Partial Pressures


  The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone
• Mole Fraction


  The ratio of moles of a substance to total moles in a mixture
• Pressure and Mole Fraction

  The partial pressure of a gas is proportional to its mole fraction
• Main Tenets of Kinetic-Molecular Theory

  • Gases consist of large numbers of molecules that are in continuous, random motion
  • The combined volume of all the molecules of the gas is negligible relative to the total volume
  • Attractive and repulsive forces between gas molecules are negligible
  • Energy can be transferred between molecules during collisions, but the average kinetic energy does not change with time
  • The average kinetic energy of the molecules is proportional to the absolute temperature
• How Fast Do Gas Molecules Move?

  • Temperature is related to their average kinetic energy
  • Individual molecules can have different speeds of motion
  • u_mp is the most probable speed, u_av is the average speed, u_rms is the root-mean-square speed associated with their average kinetic energy