Phase equilibria

• what is a phase?

  state of matter that is uniform throughout, not only in chemical composition but in its physical state
• what is the equilibrium between a solid/liquid and its vapour determined by?


  vapour pressure of the substance
• high vapour pressures = volatile
• what do lines on a phase diagram represent?

  equilibrium
• what does the phase rule tell us?

  The number of parameters that can varied independently without distrubing the number of phases present in the system
• what is the equilibria of a single phase shown as on a phase diagram?

  an area
• what can be varied in a single phase?

  temperature and pressure independently
• how are two phases in equilibria shown on a phase diagram?

  as a line
• how are three phases in equilibria shown on a phase diagram?

  by a point
• what is the supercritical phase?


  Properties of a liquid at high pressure and properites of a gas at low pressure
• what is raoults law?

  that the contribution of a single component to the total vapour pressure is proportional to its vapour pressure in its pure state
• what does henry law describe?

  dilute components
• units of K?


  pascals
• how does K differ from Pa*?


  solute-solvent interactions at low conc are different from solvent-solvent interactions that dominate at high conc
• what does it mean if there is more vapour than liquid on pressure-composition diagrams?

  more volatile
• what does the lever rule tells us?


  Distrubtion of components between the liquid and vapour phases for a given composition and pressure within the system
• if length of the tie lines from a,p1 to liquid to vapour are long this means?

  number of moles is large
• How is distillation understood?

  Using temperature-composition phase diagrams
• what are azeotropes?


  If there is a maximum or minimum in boiling point curve not at either 100% A or B indicates interaction of components of the mixtire
• what is the maximum boiling point azeotrope?

  • Phase diagrams showing a maximum indicate the mixture is stabilised compare to ideal solution
• what is minimum boiling point azeotrope?

  Phase diagrams showing a minimum indicate the mixture is destabilised compared to the ideal solution
• what occurs to nitrobenzene as hexane is added?

  Blue -> purple -> forms separate layer of pink -> fully pink
• why is there a separate state, hexane and nitrobenzene?


  two separate phases form:

  • nitrobenzene saturated with hexane
  • hexane saturated with nitrobenzene
• when does separation not occur?

  upper consulate temperatures
• What is a lower consulate temperature?


  low temperatures phases are more miscible because they form weak complex
• what happens when systems show lower and upper consulate temperatures?


  the miscibility of the two phases depends on a complex balance of temperature-driven formation and destruction of complexes of the two components
• what may occur when two metals are mixed?


  become partially miscible

  • two molten metals are completely miscible so form a single phase
  • meet at eutectic point