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Thermodynamics (Black Body Radiators (Black Body = body that absorbs all…

- - - - Substance will be same temperature in both phases
- - - - Molecules vibrate around fixed positions in a regular lattice
      - Molecules held in position by strong forces of attraction
    - - Molecules constantly moving around
      - Molecules free to move past one another
      - Molecules attracted to each other
    - - Molecules free to move around with constant random motion
  - - - Gas molecules in random motion
      - Molecules assumed to have no volume
      - No forces between molecules
      - All collisions elastic
    - - Gas Laws
        
        Boyle's Law: pV = constant at constant temperature
        
        reducing volume causes molecules to be closer together ∴ will collide with each other and the container more often ∴ pressure increases
        
        Charles's Law: V/T = constant at constant pressure
        
        when gas is heated, molecules gain KE which at constant pressure means they move more quickly and further apart ∴ volume increases
        
        Capillary tube sealed at bottom with drop of conc. sulphuric acid inside that traps air column between bottom of tube and droplet
        
        fill beaker with near-boiling water + regularly record temperature of water + air column length as the water cools - as water cools, length decreases
        
        repeats + take averages
        
        Pressure Law: P/T = constant at constant volume
        
        when gas heated, molecules gain KE ∴ move faster. Pressure constant ∴ molecules collide with each other and container more often and at higher speeds ∴ pressure increases
  - - - A gas molecule of mass m is bouncing off the wall. If it hits the wall at speed u, its momentum approaching the wall is mu. Assuming the collisions are perfectly elastic, it rebounds and heads in the opposite direction with speed u ∴ change in momentum = 2mu
        
        Assuming particle doesn't collide with any other particles, time between collisions of Q and the wall = 2x/u ∴ number of collisions per second = u/2x ∴ rate of change of momentum = muu/x = force
        
        only applies to one particle
        
        Pressure = force/area = (muu/x)/yz = muu/xyz where xyz = V, volume of cube ∴ P = muu/V
        
        In whole box there are N molecules and on average, 1/3 are striking each pair of faces ∴ pV=1/3Nm<"c sq">
        
        For one mole of gas:
        pV=N(a)m<"c sq"> where N(a) = Avogadro's constant
        ∴ pV=2/3N(a)*KE
        
        pV=nRT but n=1 ∴ pV=RT
        ∴ KE=3/2(R/N(a))T
        R/N(a) = k
        ∴ KE=3/2kT
- - - - L = latent heat
    - - Energy needed to break bonds that hold the molecules in place (solid to liquid)
    - - Energy needed to break bonds between the molecules when changing state from liquid to a gas