CHEMISTRY

• Pressure


  Force per unit area

  
• P


  Pressure (pascals) Pa or N/m2

  
• F


  Force (Newtons) N
• A


  Area m2
• Pressure Units


  • pascal (Pa) - 1 Pa = 1 N/m2
  • kilopascal (kPa) - 1 kPa = 1000 Pa
  • pounds per square inch (psi) - air pressure at sea level is ~14.7 psi
  • atmosphere (atm) - 1 atm = 101,325 Pa, air pressure at sea level is ~1 atm
  • bar (bar, or b) - 1 bar = 100,000 Pa (exactly), commonly used in meteorology
  • millibar (mbar, or mb) - 1000 mbar = 1 bar
  • inches of mercury (in. Hg) - 1 in. Hg = 3 386 Pa, used by aviation industry, also some weather reports
  • torr - 760 torr= 1 atm, named after Evangelista Torricelli, inventor of the barometer
  • millimeters of mercury (mm Hg) - 1 mm Hg ~1 torr

  
• Converting 29.2 in. Hg to other pressure units

  741.595 torr = 742 torr

  1. 0.976 atm
  2. 98.87 kPa = 98.9 kPa
  3. 988.7 mbar = 989 mbar
• Gauge pressure


  The pressure of the fluid alone

  
• Absolute pressure


  The total pressure, including atmospheric pressure

  
• Barometer


  A scientific instrument used to measure air pressure

  
• Manometer


  An open ended instrument filled with liquid to measure gas pressure

  
• Amontons's Law / Gay-Lussacs Law


  Pressure is directly proportional to temperature (in Kelvin)

  
• Charles's Law


  Volume is directly proportional to temperature (in Kelvin)

  
• Boyle's Law


  Volume is inversely proportional to pressure

  
• Avogadro's Law


  Volume is directly proportional to number of moles
• Ideal Gas Law


  Combines the gas laws: PV = nRT
• Standard conditions of temperature and pressure
• Boyle's Law


  When volume decreases, gas pressure increases due to increased frequency of molecular collisions

  
• Avogadro's Law


  When the amount of gas increases at a constant pressure, volume increases to yield a constant number of collisions per unit wall area per unit time

  
• Amonton's Law


  When gas temperature increases, gas pressure increases due to increased force and frequency of molecular collisions

  
• Kinetic molecular theory (KMT)


  A simple microscopic model that effectively explains the gas laws
• Postulates of kinetic molecular theory

  • Gases are composed of molecules that are in continuous motion, travelling in straight lines and changing direction only when they collide with other molecules or with the walls of a container
  • The molecules composing the gas are negligibly small compared to the distances between them
  • The pressure exerted by a gas in a container results from collisions between the gas molecules and the container walls
  • Gas molecules exert no attractive or repulsive forces on each other or the container walls; therefore, their collisions are elastic (do not involve a loss of energy)
  • The average kinetic energy of the gas molecules is proportional to the kelvin temperature of the gas
• Diffusion


  Movement of an atom or molecule from a region of relatively high concentration to one of relatively low concentration
• Effusion


  The transfer of gaseous atoms or molecules from a container to a vacuum through very small openings
• Graham's law of effusion

  The rate of effusion of a gas is inversely proportional to the square root of the mass of its particles

  
• Molar mass of CO2 is 44 g/mol
• Molar mass of CH4 is 16 g/mol
• Molar mass of O2 is 32 g/mol
• An unknown gas effuses 1.66 times more rapidly than CO2. The molar mass of the unknown gas is 16 g/mol
• Decompression sickness, also known as the bends, is a condition that can occur in scuba diving

  
• Greenhouse gases contribute to climate change