Chapter 7 Slides

• Oral medicine syringe with no needle

  • Plunger can be drawn all the way out to fill with air
  • Placing finger over open tip and depressing plunger "squeezes" the sample of air
• The particles of a gas are usually far apart; a sample of gas is mostly empty space
• Squeezing air in the syringe

  1. Space between the particles is decreased

  2. Particles of air are forced closer together
• Pressure


  A force exerted against a given area
• Units of air pressure

  • Atmosphere (atm)
  • Pascal (Pa)
  • Pounds per square inch (psi)
  • Millimeters of mercury (mmHg)
• Atmosphere (atm)


  Unit of air pressure
• Pascal (Pa)


  SI unit of pressure
• Pounds per square inch (psi)


  Measures pressure as the force (measured in pounds) applied to an area of 1 square inch
• Millimeters of mercury (mmHg)


  Unit used when measuring blood pressure, comes from the mercury barometer which measures the pressure of the earth's atmosphere
• The pressure of the atmosphere at sea level is about 14.7 psi
• Pressure


  Force per unit Area
• Atmospheric pressure (atm)


  P = F/A
• Atmospheric pressure is the result of the weight of air acting on the earth's surface
• Mercury barometer


  A long, sealed glass tube with liquid mercury inverted into a dish of mercury without letting air into the tube
• Mercury barometer


  • The force of the atmosphere pushing down on the mercury in the dish prevents the mercury in the tube from draining out
  • If the tube is long enough, a column of mercury 760 mm high (29.92 in) will remain inside the tube at sea level
• The height of the mercury column gives us the pressure in mmHg so the barometer is a tool to measure atmospheric pressure
• All gases, such as oxygen gas (O2), nitrogen gas (N2), carbon dioxide gas (CO2), and other gases, behave similarly
• Kinetic molecular theory of gases


  Explains the unique behaviors of gases
• Ideal gas


  A gas that perfectly adheres to the kinetic molecular theory of gases
• Assumptions of the kinetic molecular theory

  • Gas particles are far apart from each other; most of the volume of a gas is empty space
  • Gas particles are in constant, random motion, having a range of speeds
  • Gas particles have no attractive forces between them
  • Gas particles are moving and therefore have kinetic energy. This energy is directly proportional to the absolute temperature. Gas particles move more quickly at higher temperatures
• These assumptions about gas behavior allow us to quantify relationships as gases change conditions like pressure, volume, temperature and amount of gas
• Boyle's Law


  Relationship between pressure and volume of a gas at constant temperature
• Irish chemist Robert Boyle began to experiment with the effect of pressure on the volume of a gas


  Mid-1600s
• Boyle's discovery

  • When the pressure on a gas was doubled, the volume of the gas was reduced to half of its initial volume
  • The volume of a fixed amount of gas at constant temperature is inversely proportional to the pressure
• Boyle's Law


  1. Determine the given information

  2. Solve for the missing variable using the Boyle's law relationship

  3. Substitute the given information into the equation and solve

  4. Check your answer
• As pressure decreases, volume increases and vice versa
• Pi


  Initial or starting pressure
• Vi


  Initial or starting volume
• Pf


  Final or ending pressure
• Vf


  Final or ending volume
• Pi x Vi = Pf x Vf
• Charles's Law


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

  • If the pressure and amount of a gas are not allowed to change, the volume of the gas is directly proportional to its absolute temperature
  • When the absolute temperature of a gas is doubled, the volume of the gas is also doubled
• Applying Charles's Law

  1. Determine the given information

  2. Convert temperatures to absolute temperature scale (Kelvin)

  3. Solve for the missing variable using the Charles's law relationship

  4. Substitute the given information into the equation and solve

  5. Check the answer makes sense
• Charles's Law was discovered by French scientist Jacques Charles through experiments with gases
• Gay-Lussac's Law


  When the temperature increases, the gas particles move faster and hit the walls of their container more frequently, increasing the pressure
• Gay-Lussac's Law

  Observe changes in pressure and temperature in various gases
• Gay-Lussac's Law


  • Can be used to determine what will happen to a sample of gas of known pressure and temperature if we make changes to either pressure or temperature
• Ideal Gas Constant, R


  0.08206 L · atm/mol · K
• n


  Number of moles