Particle model of matter

• Solid

  • Strong forces of attraction hold the particles close together in fixed, regular arrangement.
  • Particles don't have that much energy so only vibrate
  • Density is generally highest in this state as particles are close together
• Liquids

  • Weaker forces of attraction between the particles
  • Particles are close together nut can move past eachother and form irregular arrangements
  • more energy than particles in a solid- move in random directions at low speeds
  • Genereally less dense than solids
• Gases

  • Almost no forces of attraction between the particles
  • Particles have high energy
  • Particles are free to move, and travel in random directions at high speeds
  • Less dense than liquids
• Internal energy


  The total energy that the particles in a system have in their kinetic and potential energy stores

  Heating the system transfers energy to its particles increasing the internal energy
• Measuring density of a liquid

  1. Place a measuring cylinder on a balance and zero the balance
  2. Pour 10ml of the liquid into the measuring cylinder and record the liquids mass
  3. Pour another 10ml into the measuring cylinder, repeating the process until the cylinder is full and recording the total volume and mass each time.
  4. For each measurement us the formula mass/volume to find out the density of the liquid
  5. Finally, take an average of your calculated densities. This will give you a value for the density of the liquid
• Density


  The mass per unit volume of a material

  How closely packed the particles are
• Measuring density of a solid

  1. Use a balance to measure its mass
  2. If its a regular solid, start by measuring the LxWxH to give you the volume
  3. For an irregular solid, you find its volume by submerging it into a eureka can filled with water. The water displaced by the object will be transferred to the measuring cylinder
  4. Then to find the objects density divide the mass by the volume
• Specific latent heat


  The amount of energy needed to change 1kg of a substance from one state to another without changing its temperature
• Specific latent heat of fusion


  The specific latent heat for changing between a solid and a liquid
• Formula for specific latent heat


  Energy= mass x specific latent heat
• Specific latent heat of vaporisation


  Specific latent heat for changing between a liquid and a gas
• Density


  The mass per unit volume of a material
• Density equation


  1. ⍴=m/v

  2. Density (kg/m³)

  3. Mass (kg)

  4. Volume (m³)
• States of matter in order of 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
• Mass is always conserved when a substance undergoes a change of state
• 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
• Sublimation


  A solid changes into a gas without passing through a liquid state
• Evaporation


  A liquid changes into a gas state
• Condensation


  A gas changes into a liquid state
• Water boils in an open pan

  Some of the water will evaporate and turn into water vapour, leaving the pan and decreasing the mass of the pan. The mass of the whole system however remains constant.
• 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
• Motion of molecules in a gas

  In constant random motion
• Factor affecting average kinetic energy of gas molecules


  • 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
• Gas A at low pressure, Gas B 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 gas pressure 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
• Product of pressure and volume for fixed mass of gas at constant temperature
• Unit for pressure


  Pascal (Pa)
• Doing work on a gas


  • Increases the internal energy of the gas
  • Can also lead to an increase of temperature
• Why temperature of air in 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