Particle model of matter

• density?

  The mass per unit volume of a material
• Density equation



  p/density=kg/m3

  mass= kg

  volume=m3
• states of matter increasing density

  • gas
  • liquid
  • solid
• solid

  • Tightly packed in a regular arrangement
  • Particles can only vibrate on the spot
• liquid

  • Close together, but with an irregular arrangement
  • They can flow over each other
• gas

  • Separated, with no regular arrangement
  • Particles can move freely
• What is always conserved when a substance undergoes a change of state?

  Mass
• change of state


  The material can return to having its previous properties if the change is reversed
• Chemical change
?


  The material cannot return to having its previous properties
• Bathroom mirror mists up

  1. Hot water evaporates to form water vapour
  2. This water vapour lands on the cooler mirror
  3. The vapour condenses and returns to liquid state on the mirror's surface
• Internal energy of a substance

  • The energy stored by the particles
  • The sum of the total kinetic and potential energies that make up the system
• Heating a substance


  • Transfers energy to the substance
  • Increases the energy of the particles that make up the substance
• What heating a substance can do

  • Raise its temperature
  • Change the state of the substance
• Factors that determine temperature change of a system

  • Mass of substance being heated
  • Type of material (Specific heat capacity)
  • Energy inputted into the system
• Specific latent heat



  The amount of energy needed to change the state of 1kg of a substance with no change in temperature
• Specific latent heat of fusion?

  The energy required to change 1kg of a substance from solid state to liquid state without a change in temperature
• Specific latent heat of vaporisation?

  The energy required to change 1kg of a substance from liquid state to gas state (vapour) without a change in temperature
• Factor affecting average kinetic energy of gas molecules

  • The temperature of the substance
  • The higher the temperature, the higher the average kinetic energy of the molecules
• Increasing temperature of a gas held at constant volume

  Pressure of the gas will increase
• Why pressure increases as temperature increases (at constant volume)?

  1. Kinetic energy of molecules increases
  2. Collisions between molecules becomes more frequent.
  3. Greater rate of change of momentum
  4. Greater force and therefore pressure
• If gas A is at low pressure, and gas B is at high pressure


  • There are more collisions per second in gas B than in gas A
  • The rate of collisions is higher in B
• Force exerted by pressure of gas on container walls

  • The net force acts at right-angles to the container's surface
  • The force increases as pressure increases
• How increasing volume of gas results in decreased pressure?

  1. Molecules become more spread out and so time between collisions increases.
  2. This reduces the rate of collisions
  3. Rate of change of momentum decreases, and so force exerted on container decreases, resulting in a lower pressure
• Unit for pressure



  pascal (Pa)
• What increases when you do work on a gas?

  • The internal energy of the gas
  • This can also lead to an increase of temperature
• Why temperature of air inside a bike pump increases when pumped

  1. Work is done on a gas when it is compressed
  2. Doing work on a gas increases its internal energy, so also increases the average kinetic energy of the molecules
  3. Temperature increases with an increase of average kinetic energy