Chemistry Final

• Properties of each phase are determined by the balance between potential and kinetic energy of particles
• Potential energy, in the form of attractive forces, tends to draw particles together
• Kinetic energy, associated with movement, tends to disperse particles
• Intramolecular or bonding forces are found within a molecule
• Intermolecular or nonbonding forces are found between molecules
• Physical behavior of each phase of matter is different because the strength of these forces differ from state to state
• Gas:

  • Conforms to shape and volume of container
  • High compressibility
  • High ability to flow
• Liquid:

  • Conforms to shape of container; volume limited by surface
  • Very low compressibility
  • Moderate ability to flow
• Solid:

  • Maintains its own shape and volume
  • Almost none compressibility
  • Almost none ability to flow
• Gas:

  • Attractive forces are weak relative to kinetic energy
  • Particles are far apart
  • A gas has no fixed shape or volume
• Liquid:

  • Attractive forces are stronger because particles have less kinetic energy
  • A liquid can flow and change shape, but has a fixed volume
• Solid:

  • Attractions dominate motion
  • Particles are fixed in place relative to each other
  • A solid has a fixed shape and volume
• Enthalpy changes accompany phase changes
• Energy must be absorbed by the system to overcome the attractive forces that keep the particles in a liquid together and those that keep them fixed in place in a solid
• For vaporization: heat of vaporization (∆H°vap)

  For fusion: heat of fusion (∆H°fus)
• ∆H°vap is always larger than ∆H°fus because it takes more energy to separate particles completely than just to free them from their fixed positions in the solid
• Phase change is a change in intermolecular distance and freedom of motion
• Sublimation: solid to gas

  Deposition: gas to solid

  Heat of sublimation (∆Hsubl) - the enthalpy change when 1 mol of a substance sublimes
• Fusion (or melting), vaporization, and sublimation are endothermic changes (positive ∆H°)

  Freezing, condensation, and deposition are exothermic changes (negative ∆H°)
• Within a phase, heat flow is accompanied by a change in temperature, since the average Ek of the particles changes
• In a closed flask, the system reaches a state of dynamic equilibrium, where molecules are leaving and entering the liquid at the same rate
• Vapor pressure is the pressure exerted by the vapor on the liquid
• Factors affecting Vapor Pressure:

  • As temperature increases, the fraction of molecules with enough energy to enter the vapor phase increases, and the vapor pressure increases
  • The weaker the intermolecular forces, the more easily particles enter the vapor phase, and the higher the vapor pressure
• Vapor pressure increases as temperature increases

  Vapor pressure increases as the strength of the intermolecular forces decreases
• Boiling point of a liquid is the temperature at which the vapor pressure equals the external pressure
• Normal boiling point of a substance is observed at standard atmospheric pressure or 760 torr
• Phase diagram combines the liquid-gas, solid-liquid, and solid-gas curves to describe the phase changes of a substance at various conditions of temperature and pressure
• Each region in the phase diagram represents 1 phase that is stable for any combination of pressure and temperature within its region
• Each line in the phase diagram shows conditions for each phase transition and the pressure and temperature at which the 2 phases exist in equilibrium
• Critical point is where the liquid-gas line ends, and the critical temperature (Tc) and critical pressure (Pc) are defined
• Triple point is the pressure and temperature at which the three phases are in equilibrium
• At the triple point, the substance is subliming & depositing, melting & freezing, and vaporizing & condensing simultaneously
• Surface tension is the energy required to increase the surface area of a liquid
• The stronger the forces between particles, the higher the surface tension
• Water has a high surface tension due to multiple hydrogen bonds
• Surfactants (surface-active agents) like soaps, petroleum recovery agents, and biological fat emulsifiers decrease the surface tension of water by congregating at the surface and disrupting the hydrogen bonds
• Capillarity is the rising of a liquid through a narrow space against the pull of gravity (capillary action)
• Capillarity results from a competition between cohesive forces within the liquid and adhesive forces between the liquid and the tube walls
• Water displays a concave meniscus, while mercury displays a convex meniscus
• Glass is mostly silicon dioxide (SiO2) and water molecules form hydrogen bonds to the oxygen atoms of the tube's inner wall