physics - kinetic theory

• Pressure


  A measure of how spread out a force is over a surface
• Pressure


  • Force is measured in Newtons (N)
  • Area is measured in m² or cm²
  • Pressure is measured in N/m² or N/cm²
  • Pressure can also be measured in Pascals (Pa). 1 N/m²=1Pa
• Large area


  Less pressure, e.g. snow boots have less pressure than high heels
• Kinetic theory


  The idea that gases consist of lots of tiny particles constantly moving in random directions
• Kinetic theory


  1. Molecules of gas collide with the surface of an object

  2. This creates a pressure

  3. Molecules don't lose any energy when they collide with the surface or with each other
• As volume increases


  Pressure decreases at a decreasing rate
• As temperature increases


  Pressure increases
• As temperature increases


  Volume increases
• Combining pressure, volume and temperature relationships

  PV = P₁V₁/T₁ = P₂V₂/T₂
• Absolute zero


  The point where there is no pressure, where the particles have no energy and do not move, at -273°C
• Absolute temperature


  Measured in Kelvin (K) instead of Celsius (C), where 0°C = 273K
• Specific heat capacity


  How much heat energy is needed to increase the temperature of 1kg of a substance by 1 degree
• Specific latent heat


  The amount of heat energy needed to change 1kg of a substance from one state to another
• The latent heat of vaporisation is higher than fusion because more bonds are broken going from liquid to gas
• Explaining the temperature-energy input graph

  1. Between A and B: solid being heated, temperature increases

  2. Between B and C: solid melting into liquid, temperature constant (latent heat of fusion)

  3. Between C and D: liquid being heated, temperature increases

  4. Between D and E: liquid turning into gas, temperature constant (latent heat of vaporisation)
• 1 Pa = 1 N/m²
• Absolute zero


  The point where pressure and temperature reach 0, at -273°C
• Temperature


  Measure of the average kinetic energy of the particles in a substance
• How the temperature of a block of ice changes over time as it is heated

  1. A-B: Solid

  2. B-C: Melting

  3. C-D: Liquid

  4. D-E: Boiling

  5. E-F: Gas
• Specific heat capacity


  The energy required to heat 1kg of a substance by 1°C
• Water has a specific heat capacity of 4200 J/kg°C
• AQ


  Change in thermal energy
• c


  Specific heat capacity
• ΔT


  Change in temperature
• Solid state


  • Particles are packed very closely, vibrate in place but are not free to move
• Liquid state


  • Particles are close together but can move, energy is used to break some of the bonds holding the particles in place
• Gas state


  • Particles are free to move and have large gaps between them, energy is used to break all the bonds holding the particles in place
• Specific latent heat


  The energy required to change the state of 1kg of a substance without a change in temperature
• Ice has a specific latent heat of fusion of 3,360,000 J/kg
• As it is heated


  The specific latent heat of fusion is larger than the latent heat of vaporisation because more bonds are broken when particles move past each other more quickly
• The specific latent heat of vaporisation is larger than the latent heat of fusion
• As it is heated, the particles move more quickly
• Q


  Thermal energy for change in state
• L


  Specific latent heat