gases

• Gases


  • Can be compressed
  • Exert pressure on whatever surrounds them or its container
  • Expand into whatever volume is available
  • Mix completely with one another
  • Described in terms of temperature, pressure, volume occupied, and the amount of gas present
• Kinetic-Molecular Theory of Gases


  • Explains the common behavior and properties found among gases
• Kinetic-Molecular Theory of Gases

  1. Gases can be compressed

  2. Gases exert pressure on whatever surrounds them or its container

  3. Gases expand into whatever volume is available

  4. Gases mix completely with one another

  5. Gases are described in terms of their temperature and pressure, the volume occupied, and the amount of gas present
• Postulates of the Kinetic-Molecular Theory

  • A gas is composed of molecules whose size is much smaller than the distances between them
  • Gas molecules move randomly at various speeds and in every possible direction
  • Except when gases collide, forces of attraction and repulsion between them are negligible
  • When collisions between molecules occur, the collisions are elastic
  • The average kinetic energy of gas molecules is proportional to the absolute temperature
• Ideal Gases


  • Behave exactly as described by equations relating pressure, volume, temperature, and amount of gas
  • Most gases behave nearly ideally at room temperature and atmospheric pressure
  • Equations describing the relationship among the 4 variables of gases are called Gas Laws
  • Include Pressure-volume (Boyle’s Law), Temperature-pressure (Charles’s Law), Amount-volume (Avogadro’s Law), Law of Combining Volumes (Gay-Lussac’s Law), and the Ideal Gas Law
• Ideal Gas Law


  Summarizes the relationship among volume, temperature, pressure, and amount using the equation PV = nRT
• When applying stoichiometry to gases, the law of combining volumes and the ideal gas law allow the use of volumes as well as masses or molar amounts in calculations
• Kinetic-molecular Model of Liquids

  • Properties of liquids understood on the molecular, nanoscale level
  • Strength of interaction among molecules, atoms, or ions account for physical properties
  • Liquids can flow and fill a container like gases
  • With sufficient energy, liquids can change phase
• Intermolecular Forces

  • Attractive and repulsive forces between molecules of a substance
  • Responsible for most physical and chemical properties of matter
  • Responsible for the condensed states of matter
  • Particles in solids and liquids are held together by intermolecular forces
• Dipole-dipole


  • Attractive forces among polar molecules
• Intermolecular forces are responsible for the most of the physical and chemical properties of matter
• Intermolecular forces are responsible for the condensed states of matter
• The particles making up solids and liquids are held together by intermolecular forces
• Dipole-dipole


  • Attractive forces among polar molecules
  • Polar molecules have permanent dipoles formed due to differences in electronegativities of the atoms
  • The partially positive portion of one molecule is attracted to the partially negative portion of another molecule
• Ion-Dipole


  • Similar to dipole-dipole but arise between ions and polar molecules
• Dispersion


  • The weakest force arising from the movement of electrons creating temporary positive and negative charged regions
• Hydrogen bond


  • A special type of dipole-dipole attraction between molecules, not a covalent bond to a hydrogen atom. It results from the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as a N, O, or F atom and another very electronegative atom
• Intermolecular forces and Properties of Liquids

  1. Intermolecular forces play a large role in many physical properties of liquids

  2. Surface Tension

  3. Viscosity

  4. Capillary Action

  5. Vapor Pressure
• Surface Tension

  • The energy required to expand a liquid surface
  • Higher for liquids with strong intermolecular forces
  • Prevents objects from breaking through the surface and sinking
  • Accounts for the nearly spherical shape of rain droplets
• Capillary Action


  • The process of liquid flowing through a narrow space opposing the force of gravity
  • Made possible by the combined effects of cohesion, adhesion, and surface tension
• Viscosity


  • The resistance to flow of a liquid
  • Related to its intermolecular forces
  • Decreases when temperature increases as kinetic energy among atoms surpasses the intermolecular forces
• Vapor Pressure


  • The measure of a liquid's volatility
  • Directly related to temperature
  • Increase in temperature allows most molecules to exceed the energy threshold required to change phases (liquid to gas)