Macroscopic Properties of Gases

• Pressure


  The amount of force applied by gas molecules perpendicularly per unit area
• Volume


  Gases do not have a definite volume, they will always occupy the space inside their containers
• Temperature


  The average kinetic energy of the gas particles
• Gases are constantly moving due to the space between them, and each gas molecule possesses a certain amount of kinetic energy that defines its motion
• Decreasing the volume of gases increases their pressure
• Macroscopic properties of gases

  • Volume
  • Temperature
  • Pressure
  • Amount of gas in moles
• Pascals (Pa)


  The SI unit for pressure, equal to 1 Newton per square meter (N/m^2)
• Atmosphere (atm)


  A unit of pressure defined as the pressure observed at sea level, equivalent to 101,325 Pa
• Bar


  The standard condition for pressure defined by IUPAC, equivalent to 100,000 Pa
• Measuring the total force exerted by gas molecules is difficult, so instruments like barometers and manometers are used to indirectly measure the pressure of gases by comparing them with liquid pressures
• The first barometers used liquid mercury to measure the pressure, which is where the unit mmHg (millimeters of mercury) came from
• Pressure is a macroscopic property of gas because it describes the gas as a whole, not as individual particles
• Blaise Pascal, a physicist who studied the pressure based on the principles of hydraulics, is the namesake of the SI unit of pressure, the Pascal (Pa)
• Factor-label method/Dimensional analysis


  A method used to convert between different units of pressure, where the conversion factor is expressed as a fraction with the given unit in the denominator to cancel it out
• Blaise Pascal


  Physicist who studied pressure based on the principles of hydraulics
• Blaise Pascal's experiments


  1. Studied Earth's atmosphere using a mercury barometer

  2. Showed that at increasing heights, air pressure must be lower compared to the surface
• Pressure


  The amount of force applied per unit area
• Pressure is used as a macroscopic property of gas because it is impossible to measure the total force of each gas molecule in a container for practical purposes
• The units of pressure applied depends on the constants that you will be working with on mathematical equations involving gases
• Converting pressure units


  1. Identify what is being asked

  2. Identify what is given

  3. Write the equation needed to convert

  4. Substitute the given values

  5. Solve for the pressure in the new unit
• In the factor-label method, you need to express the conversion factor as a fraction. The given unit should be in the denominator such that it cancels out the unit of the given
• Converting pressure units


  • 2.5 atm to bar
  • 10.00 atm to mmHg
  • 450 torr to Pa
  • 3.00 kPa to bar
• Macroscopic properties of gases


  • Temperature (measure of average kinetic energy of gas particles)
  • Volume (space occupied by gas molecules)
  • Pressure (force applied per unit area)
• Pressure is defined as the force that gas molecules apply on the walls of their container
• Pressure unit conversions


  • atm
  • kPa
  • bar
  • torr
• It is possible to convert a unit of pressure to another without converting it first to atm
• Force applied


  Pressure exerted (force per unit area)