Thermal Properties

Direction of thermal energy transfer between 2 objects is determined by temperature (temp is proportional to avg KE of particles in the substance) when bodies are in thermal contact. After enough contact thermal equilibrium is reached (temp of 2 bodies is the same).

Tk = Tc + 273.15

Heat = energy transfered from one body and into another as a result of a difference in temperature during a thermal interaction ... Hot to Cold.

Internal Energy = total KE of the molecules of a substance, plus any PE associated with forces between the molecules.

KE is the movement of particles and PE is associated with the binding forces of the particles ... the tighter the bond the lower the PE.

gases solids
High KE Low KE molecules "vibrate"

 

 

Specific Heat Capacity, c : The amount of heat needed to raise the temp of a mass of one kg of a substance by one kelvin.

Q = mc(delta T)

Heat Capacity. C = mc ... amount of thermal energy required to change the temperature of a substance by one Kelvin. Used when there are many substances combined together.

 

 

Physical differences of Solid, Liquid and Gas

  molecular structure particle motion
solid
  • fixed volume, fixed shape
  • held together by bonds
each molecule vibrates around a mean position
liquid
  • fixed volume, varying shape
  • strong bonds to keep molecules close, but they are free to move around each other
molecules vibrate but not fixed in positoin (free movement)
gas

 

  • always expands to fill space of containerweak forces
  • no fixed position
random motion

 

Phase Changes

  • Melting: solid to liquid
  • Freezing: liquid to solid
  • Boiling: liquid to gas
  • Evaporation: liquid to gas
  • Condensing: gas to liquid

 

Temperature does not change during phase change. Energy given to molecules does not change the KE (temp) therefore it changes the PE (bonds). All energy is used to break intermolecular bonds.

Difference between evaporation and boiling.

  • Evaporation: happens slowly and from the top. Only the fastest molecules that are near the surface leave and therefore the average KE of the remaining molecules is reduced.
  • Boiling: happens fast, from the bottom and bubbles created. Molecules from anywhere within the liquid can escape.

Specific latent heat of fusion, Lf : Thermal energy required to melt a unit of mass of material at its melting point. Q = mLf

Specific latent heat of vaporization, Lv : Thermal energy required to vaporize a unit of mass of material at its boiling point. Q = mLv