Physics P3 Particle Model of Matter

• Pressure in gases


  Physics only
• Increasing the pressure of a gas

  Physics only - Higher Tier
• Density is the mass of a given volume of a substance
• Density


  Determined by the mass of the atoms it is made from and how closely these atoms are packed together
• Substance densities


  • Water (l): 1 000 kg/m3
  • Glass (s): 3 140 kg/m3
  • Iron (s): 7 700 kg/m3
  • Aluminium (s): 2 800 kg/m3
  • Hydrogen (g): 0.085 kg/m3
• Density


  • Solids have particles packed close together
  • Liquids have particles free to move so the same mass takes up more space
  • Gases have particles taking up a much greater volume than liquids and solids
• For any particular substance, a solid is usually denser than its liquid and the liquid is usually denser than the gas
• Solid water (ice) is less dense than liquid water, which is why ice floats on water
• Finding the density of an irregular object

  1. Place object in known volume of water and measure amount of water displaced, which equals the volume of the object

  2. Then calculate density using mass and volume
• A change of state can be brought about by changing the temperature or pressure of a material
• Mass is conserved when a substance changes state, only the volume changes
• Changes of state are physical changes, not chemical changes
• Physical changes can be reversed, chemical changes cannot
• Changes of state


  • Melting
  • Evaporating
  • Deposition
  • Subliming
  • Condensing
  • Freezing
• Determining volume of irregular object

  Place object in known volume of water and measure amount of water displaced, which equals the volume of the object
• Internal energy is the energy stored in a system by the atoms and molecules that make up that system
• Internal energy


  Total kinetic and potential energy of particles in a system
• When heat is added to a system, the internal energy of the particles increases, which can result in the material changing state
• Specific heat capacity (c)

  Energy required to raise the temperature of 1 kg of a substance by 1°C
• Latent heat


  Energy needed to change the state of a substance without a change in temperature
• Specific latent heat of fusion (Lf)

  Latent heat for melting
• Specific latent heat of vaporisation (Lv)

  Latent heat for evaporating
• As heat energy is added, temperature rises until melting point, then all energy goes to changing state with no temperature change, then temperature rises again until boiling point
• Internal energy

  The total kinetic and potential energy of all the particles within a system
• Changing the internal energy of a stone

  Heating it
• Water and isooctane both boil at 100 °C, but isooctane boils first when the same mass of each is placed on a heater
• Reason why isooctane boils first

  Isooctane has a lower specific heat capacity than water so less heat energy is needed to raise its temperature to its boiling point
• Calculating temperature rise of water


  1. ΔE = m c Δθ

  2. Δθ = ΔE / (m x c)

  3. Δθ = 25 200 / (0.2 x 4200) = 30 °C
• Latent heat

  The energy needed to change the state of a substance without changing the temperature
• Latent heat of fusion

  The energy needed to change between solid and liquid
• Latent heat of vaporisation

  The energy needed to change between liquid and gas
• Calculating heat energy needed to melt a 250 g candle


  1. E = m Lf

  2. E = 0.25 x 200 000 = 50 000 J
• Brownian motion


  Constant random motion of molecules in a gas
• Temperature of a gas

  Related to the average kinetic energy of the particles
• Increasing temperature of a gas

  Particles move faster
• Faster moving gas particles

  Exert greater force on container walls
• Heating a sealed can of air

  Air molecules move faster, increasing pressure on can walls
• Gas pressure is directly related to temperature if volume remains constant
• Pressure in a gas

  Caused by collisions of gas particles on container walls
• Compressing a gas in a fixed container

  More particles in a given volume, increasing pressure on walls