Thermal Energy Transfers

• States of matter


  • Solid
  • Liquid
  • Gas
• Kinetic theory of matter


  A model that attempts to explain the properties of the three states of matter
• In the kinetic theory model, particles are assumed to be small spheres
• Water has three states of matter; solid ice, liquid water and gaseous steam
• The difference between each state of matter is the arrangement of the particles
• Particles in a solid

  • Closely packed
  • Arranged in a fixed pattern (lattice structure)
  • Can only vibrate about their fixed positions
  • Have low energies compared to particles in liquids and gases
• Molecular arrangement in a solid

  Particles are arranged in a fixed pattern, with no spaces between them, and are only able to vibrate about their fixed positions
• Properties of solids


  • Have a fixed shape (although some solids can be deformed when forces are applied)
  • Have a fixed volume
  • Are very difficult to compress
  • Have higher densities than liquids and gases
• Particles in a liquid

  • Closely packed
  • Randomly arranged (i.e. there is no fixed pattern)
  • Can flow past each other
  • Have higher energies than particles in solids, but lower energies than gas particles
• Molecular arrangement in a liquid

  Particles are arranged randomly and are able to flow past one another
• Properties of liquids


  • Do not have a fixed shape and take the shape of the container they are held in
  • Have a fixed volume
  • Are difficult to compress
  • Have lower densities than solids, but higher densities than gases
• Particles in a gas

  • Are far apart (the average distance between the particles is ~10 times greater than the distance between the particles in solids and liquids)
  • Are randomly arranged
  • Move around in all directions at a variety of speeds, occasionally colliding with each other and with the walls of the container they are in
  • Are negligible in size compared to the volume occupied by the gas
  • Have higher energies than particles in solids and liquids
• Molecular arrangement in a gas


  Particles can move around freely in all directions
• Properties of gases


  • Do not have a fixed shape and take the shape of the container they are held in
  • Do not have a fixed volume and expand to completely fill the available volume
  • Can be compressed
  • Have the lowest densities (~1000 times smaller than the densities of solids and liquids)
• Properties of the three states of matter

  • Particle arrangement
  • Space between particles
  • Particle movement
  • Particle energy
  • Substance shape
  • Substance volume
  • Substance density
• 2D diagram of particle arrangement for the three states of matter
• Density


  The mass per unit volume of an object
• Objects made from low-density materials typically have a lower mass
• Units of density


  g/cm^3 or kg/m^3
• How to calculate density

  Mass / Volume
• Gases are less dense than solids due to their molecular arrangements
• When converting a larger unit to a smaller one, you multiply (x)
• When converting a smaller unit to a larger one, you divide (÷)
• When dealing with squared or cubic conversions, cube or square the conversion factor too
• Thermodynamic (Kelvin) temperature scale

  Absolute zero refers to the lowest possible temperature, equal to 0 K or -273 °C
• Absolute zero


  The temperature at which the molecules in a substance have zero kinetic energy
• How to use the Kelvin Scale

  1. θ/°C = T/K - 273

  2. T/K = θ/°C + 273
• A change in a temperature of 1 K is equal to a change in temperature of 1 °C
• Temperature and kinetic energy


  The absolute temperature of a body is directly proportional to the average kinetic energy of the molecules within the body
• Ek = 3/2 kBT
• Internal energy


  The sum of the total kinetic energy and the total intermolecular potential energy of the particles within the substance
• As thermal energy is transferred to a substance, two things can happen: an increase in the average kinetic energy of the molecules, and an increase in the potential energy of the molecules
• What happens when a substance gains or loses thermal energy

  Internal energy increases or decreases
• Increase in internal energy

  • Increase in the average kinetic energy of the molecules (molecules vibrate and move at higher speeds)
  • Increase in the potential energy of the molecules (particles get further away from each other or move closer to each other)
• Temperature is a measure of the average kinetic energy of the molecules
• Only an increase in the average kinetic energy of the molecules will result in an increase in temperature of the substance
• Due to thermal expansion, when the temperature of a substance increases, the potential energy of the molecules also increases
• When only the potential energy of the molecules changes, the temperature of the substance does not change
• This is the case for all state changes (e.g. melting, boiling)
• A change in internal energy does not necessarily correspond to a change in temperature