gas laws

• Common compounds that are gases at room temperature are composed entirely of nonmetallic elements and have simple molecular formulas and low molar masses.
• Vapors is the term used for the gas phase of substances that can turn into gas but are liquids or solids under ordinary conditions.
• Behavior of Gaseous Substances

  1. Different gases have similar physical properties, even with different chemical properties.
  2. Gas expands spontaneously to fill a container, making its volume equal to the container.
  3. Highly Compressible
  4. Two or more gasses can form a homogenous mixture regardless of their identities and proportions.
  5. Molecules of gas only take up 0/1% of the total volume, with the rest being empty space.
• Xenon is the heaviest stable noble gas with a molar mass of 131 g/mol.
• Pressure is defined as the force divided by the area of the surface on which the force is acting.
• Gases exert pressure on any surface they contact.
• The impact of gas molecules causes an outward push against the walls of a container.
• Gases experience gravitational acceleration, but due to their small masses, their kinetic energies override the gravitational forces.
• The gases' kinetic energy prevents the particles of the atmosphere from falling on the Earth’s surface.
• Atmospheric Pressure is the force exerted by the atmosphere on a given surface area.
• Atmospheric Pressure is the result of the gravitational force pressing down the atmosphere on the Earth’s surface.
• The actual atmospheric pressure at any location depends on weather conditions and altitude.
• N (Newton) is the SI Unit for force

  kg is the SI Unit for mass

  m is the SI Unit for length
• Pa (Pascal) is the unit of pressure, equal to 1 N/m^2
• Bar is another unit of pressure, equal to 1000 Pa.
• Pounds per square inch is another unit of pressure

  • psi
  • lbs/in^2
• 100 kPa = 1 bar is atmospheric pressure at sea level
• Barometer is a glass tube more than 760 mm long that is closed at one end, completely filled with mercury, and inverted into a dish of mercury.
• The barometer was used to prove that the atmosphere has weight.
• Height of the mercury column is a measure of atmospheric pressure and changes as atmospheric pressure changes.
• Standard Atmospheric Pressure is the typical pressure at sea level
• Standard Atmospheric pressure is the pressure sufficient to support a column of mercury 760 mm high.
• Torr is another unit for millimeter of mercury (mm Hg)
• Four Variables of the Physical State of Gas

  1. Temperature
  2. Pressure
  3. Volume
  4. Moles of Gas
• Gas Laws is the equations that express the relationships among the four variables.
• Boyle’s Law

  • Pressure-Volume Relationship
  • The volume of a fixed quantity of gas maintained at constant temperature is inversely proportional to the pressure.
• Inhalation

  • The rib cage expands and the diaphragm moves downward
  • Increase in volume; Decrease in pressure
• Exhalation

  • Rib cage contracts and the diaphragm moves up
  • Decrease in volume; Increase in pressure
• Charles’s Law

  • Temperature-Volume Relationship
  • The volume of a fixed amount of gas maintained at constant pressure is directly proportional to its absolute temperature
  • Temperature must be in Kelvin.
• Avogadro’s Law

  • Quantity-Volume Relationship
  • The volume of a gas maintained at constant temperature and pressure is directly proportional to the number of moles of the gas.
• Law of Combining Volumes

  • At a given pressure and temperature, the volumes of gases that react with one another are in the ratios of small whole numbers.
• Avogadro’s Hypothesis

  • Equal volumes of gases at the same temperature and pressure contain  equal numbers of molecules.
• Ideal-Gas Law

  • A hypothetical gas whose pressure, volume, and temperature relationships are described completely by the ideal-gas equation.
  • We consider the molecules as taking up no space in the container.
• Two Assumptions of the Ideal-Gas Equation

  1. The molecules of an ideal gas do not interact with one another.
  2. The combined volume of the molecules is much smaller than the volume the gas occupies.
• The volume occupied by 1 mol of ideal gas at STP is 22.41 L.
• Gas density has a unit of mass per unit volume.
• The higher the molar mass and pressure, the denser the gas.
• The higher the temperature, the less dense the gas.
• Gas densities are directly proportional to pressure and molar mass, and inversely proportional to volume and temperature.
• A less dense gas will lie above a denser gas in the absence of mixing.