Topic 14: Particle Model

• Kinetic Theory - the idea that the particles in a gas move around randomly and randomly collide with each other
• Solids:

  • regular lattice structure
  • high density
  • vibrate around fixed positions
  • strong forces of attraction holds them close together
  • definite shape and volume
• Liquids:

  • lower density
  • weak forces of attraction so free to move around one another
  • definite compact volume but shape can change (flow to fit container)
• Gases:

  • lowest density
  • very weak forces of attraction so free to move with random motion
  • no definite volume or shape
• A closed system won't change the mass during a state change.
• Density - a measure of the mass in a given volume

  density = mass/volume
• If value of density is too high in Water Displacement Practical:

  • mass is too high ---> didn't zero/reset balance
  • volume is too low ---> didn't fill up the water level to the spout of the displacement line
• Independent Variable - what you change

  Dependant Variable - what you measure

  Control - environment to make experiment valid (same water volume in displacement can)
• Water Displacement Practical (Solid Density):

  1. Measure the solid mass using a balance
  2. Fill displacement can with water until the water just starts to come out of the spout
  3. Hold measuring cylinder under the spout and carefully place solid into displacement can
  4. If object floats, carefully push it down until all of it is submerged - finger not in water
  5. Record the volume of water displaced by the solid in the measuring cylinder
• Internal Energy - the total energy stored by the particles making up a substance or system
• Temperature is the measure of the average internal energy of a substance.

  The internal energy is the kinetic energy stored in an object so as the KE increases the temperature increases
• Specific Heat Capacity - the amount of energy needed to raise the temperature of 1kg of a substance by 1 degree
• The energy provided to a substance is being used to weaken and break the forces holding particles together - the temperature is constant during this
• Specific Latent Heat - the energy required to change 1kg of a particular substance from one state to another without changing temperature
• The problem with the Celsius scale is that it has negative numbers even though temperature is a scalar.

  The Kevin scale starts with absolute zero which is the lowest possible temperature in the universe (Kelvin 0 = -273'C)
• When particles collide with the walls of a container they change:

  • direction
  • velocity
  • momentum
  • exert a force - always at right angles to the surface
• Total pressure - how many collisions per second (frequency) and how much energy each collision involves

  Pressure = force/area
• Higher temperature increases the kinetic energy store of particles meaning more collisions per second and more energy is transferred to create a greater force so pressure increases as temperature increases
• Higher concentration in the same volume means more collisions per second so pressure increases.

  This is the same for a smaller volume but same concentration
• Specific Heat Capacity Practical (Water):

  1. Put a polystyrene cup in a beaker onto a balance then zero it
  2. Fill the cup almost to the top with water and record the mass
  3. Put a thermometer and a 12V electric immersion heater into the water - heating element completely submerged
  4. Connect immersion heater to a joulemeter
  5. Record water temperature and switch on the immersion heater - stir water with thermometer gently
  6. Record water temperature and joulemeter reading after 5 minutes
• For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume
• When work is done on a gas, the gas particles gain kinetic energy meaning they move faster and collide more frequently with greater force.

  This generates heat