Week 5 (Gases, Energy & Chemistry)

• Gases, volatile molecules (low boiling point), are part of our lives in so many ways
• Ideal gas


  A gas that perfectly follows the gas laws
• Gas Laws


  How pressure, temperature, volume and amount of substance (moles of gas) affect each other
• p1V1/T1 = p2V2/T2


  Can be used to calculate p, V or T for a given sample of gas, or any gas in a given reaction

  
• Ideal gas law


  pV = nRT
• Ideal gas law


  Can be used to calculate p, V, T, n for a given sample of gas, or any gas in a given reaction
• States of matter


  • Solid: fixed volume and shape, slightly compressible

  Liquid: no fixed shape, slightly compressible

  Gas: no fixed volume or shape, highly compressible
• At room temperature, some compounds are in the solid state and others in the liquid state
• Properties of gases


  • Uniformly fill any container

  Mix completely with any other gas

  Highly compressible

  Exert pressure on surroundings
• Gas pressure (p)


  The force exerted per unit area by the gas on the walls of its container
• Barometer is a device used to measure atmospheric pressure
• Units of pressure


  • Pascal (Pa)

  mm Hg

  atm

  bar
• 1 atm = 760 mm Hg

  1 Pa = 1 N m-2

  1 bar = 1 × 10^5 Pa = 1 × 10^2 kPa = 0.9872 atm
• Atmospheric pressure is 'pushing' on our bodies all the time
• Pressure


  Force per unit area
• Pressure units


  • Pascal (Pa)

  Atmosphere (atm)

  Bar

  Millimetres of mercury (mm Hg)

  Torr

  
• Pressure conversions


  • 380 mm Hg = 380 torr = 0.5 atm = 50662 Pa = 50.662 kPa
• Volume units


  Litre (L)

  Millilitre (mL)

  Cubic meters (m3)

  Cubic centimeters (cm3)

  Cubic decimeters (dm3)

  
• The Periodic Table shows which elements exist as gases at room temperature
• Kinetic-Molecular Theory of Gases

  Describes the behaviour of matter at the molecular or atomic level

  Explains the observable gas laws
• Principles of Kinetic-Molecular Theory

  • Gas molecules move randomly, in straight lines and collide with each other and container walls

  No forces exist between ideal gas molecules

  Volume of gas molecules is negligible compared to container volume

  Collisions are elastic (energy is conserved)

  Average kinetic energy of molecules increases as temperature increases
• All gases, regardless of molecular mass, have the same average kinetic energy at the same temperature
• Gases covered in this lecture

  • Molar volumes, density
  • Gas stoichiometry
  • Partial pressures
  • Real gases

  
• Boyle's Law: p ∝ 1/V, pV = constant
• Charles' Law: V ∝ T, V/T = constant
• Avogadro's Law: V ∝ n, V/n = constant
• Applying the simple gas law relationship


  Calculate p, V or T for a given sample of gas, or any gas in a given reaction

  
• Applying the ideal gas law: pV = nRT


  Calculate p, V, T, n for a given sample of gas, or any gas in a given reaction

  
• Temperature conversion: 0°C = 273.15 K (or 273 K)
• Pressure units and conversions

  • 1 bar = 100 kPa = 100,000 Pa
  • 1 atm = 101.325 kPa = 101,325 Pa

  
• Volume and concentration units and conversions
• Solving the ideal gas equation for a helium-filled balloon at 32.2 km height

  Rearrange the gas equation to calculate the new volume

  
• Energy


  The capacity to do work
• What should be understood and done by the end of this lecture

  • Calculate the density of an ideal gas
  • Calculate molar volume at STP and SLC for any gas
  • Use pV=nRT or molar volume in gas stoichiometry problems
  • Use Dalton's Law of partial pressures to calculate pressures of individual or all gases in a mixture
  • Explain the difference between an ideal gas and a real gas

  
• Joule (J)


  The unit used for measuring energy
• One joule (1 J) is the energy required to lift an object exactly 1 m against the force of one Newton (1 N)
• Newton


  A force that will give a 1 kg object an acceleration of 1 m s-2
• Density of gases


  Mass divided by volume
• Molar volume = volume of 1 mole of any gas at constant p and T

  
• Energy


  • Can be classified as kinetic energy (energy of motion) or potential energy (stored energy)