PROPERTIES OF SOLID

• Heating and cooling curve of a substance

  1. The total heat is the sum of each step qtotal = Σ qi

  2. The ice is heated qice = sicemΔT

  3. The ice melts to water qfus = ΔHfusm or ΔHfusn

  4. The water is heated qwater = swatermΔT

  5. The water evaporates to steam qvap = ΔHvapm or ΔHvapn

  6. The steam is heated qsteam = ssteammΔT
• Phase changes are characterized by changes in molecular order
• Unit cell is a relatively small repeating unit that embodies the structure of the solid
• Phase changes are transformations of matter from one physical state to another
• Crystal structure of a solid can be determined by x-ray diffraction
• Difference in structure of crystalline and amorphous solids

  Crystalline solids have highly regular arrangement of particles, while amorphous solids have considerable disorder in their structure
• Phase changes occur when energy is added or removed from a substance
• Amorphous Solids


  • Formed rapidly, constituent particles do not have time to align or organize into a more crystalline lattice
• Types of cubic lattices

  • Isomorphous
  • Polymorphous
  • Polytypes
• Heating/Cooling curve for water involves different steps of heating and cooling
• Phase diagrams are graphical representations of substances
• Crystalline Solids


  • Have well-defined crystal lattice, lattice is a 3D system of points designating the positions of the components that makeup a crystal
• William Henry Bragg and William Lawrence Bragg pioneered the work on X-ray crystallography and were awarded the Nobel Prize in Physics in 1915
• Under a set of conditions in the diagram, a substance can exist in a solid, liquid, or vapor (gas) phase
• The lines that serve as boundaries between physical states represent the combinations of pressures and temperatures at which two phases can exist in equilibrium
• Sublimation

  Instantly produces a gas, condensing water vapor, and creating a thick white fog
• The blue line on a phase diagram divides the liquid and gas phases, representing vaporization (liquid to gas) and condensation (gas to liquid) points
• The green line on a phase diagram divides the solid and liquid phases, representing melting (solid to liquid) and freezing (liquid to solid) points
• The triple point is the combination of pressure and temperature at which all three phases of matter are at equilibrium
• The labels on the graph represent the stable states of a system in equilibrium
• The critical point terminates the liquid/gas phase line, where the liquid and gaseous phases of a substance merge into a single phase
• Phase Diagrams


  • Graphical representation of the physical states of a substance under different conditions of temperature and pressure
  • Gives the possible combinations of pressure and temperature at which certain physical state or states a substance would be observed
• Features of a phase diagram

  • Plots pressure versus temperature
  • Divided into three areas: solid, liquid, and gaseous states
  • Boundary between liquid and gaseous regions stops at the critical temperature for the substance
• The red line on a phase diagram divides the solid and gas phases, representing sublimation (solid to gas) and deposition (gas to solid) points
• Liquified petroleum gas or liquid petroleum gas (LPG or LP gas)


  • Flammable mixtures of hydrocarbon gases
  • Used as fuel in heating appliances, cooking equipment, and vehicles
• Phase diagrams are plots of pressure versus temperature
• Melting point of water gets lower at higher pressures because solid ice is less dense than liquid water
• Supercritical fluid


  Merged single phase beyond the temperature of the critical point
• Interpreting a Phase Diagram: 1. Substance at 50 °C and 1 atm pressure is in the [state] phase. 2. Conditions for all three phases to be present are [temperature] and [pressure]. 3. Normal melting point of the substance is [temperature]. 4. Phases at 1 atm and 70 °C are [phases].
• Normal melting and boiling points


  Points when the pressure is 1 atmosphere
• Triple point of carbon dioxide is well above atmospheric pressure, making it impossible to get any liquid carbon dioxide at pressures less than 5.2 atmospheres
• When solid water melts, the liquid water formed occupies a smaller volume
• Triple point

  Temperature and pressure where all three phases are in equilibrium together
• Constructing a Phase Diagram: 1. Roughly sketch the phase diagram with labeled areas and points. 2. Above 2.0 atm and 450 K, one would see [observation]. 3. Phase changes from 50 K to 250 K at 1.5 atm are [description]. 4. At 1 atm and 350 K, [phase] exists. 5. At 1 atm and 175 K, [phase] exists.
• Crystal structure of solid phase causes solid forms of water and some substances to crystallize in a lattice with greater average space between molecules, resulting in a solid occupying a larger volume and lower density than the liquid
• At 1 atm pressure, carbon dioxide will sublime at a temperature of 197.5 K (-75.5 °C), known as "dry ice" as there is no liquid carbon dioxide under normal conditions, only the solid or the vapor
• Critical point


  Set of temperature and pressure on a phase diagram where the liquid and gaseous phases of a substance merge into a single phase