P1.2 - Changes of State

• Density tells you how much mass there is in a certain volume.
• Density (kg/m^3) = mass (kg) / volume (m^3)
• The particle theory is used to explain density differences. In 1cm^3 of a solid substance, there are more particles than the same substance of the same volume in a liquid or gas state. The densities of liquids and gases are more similar than the two compared to solids.
• Law of Conservation of Mass: particles cannot be created nor destroyed.
• Temperature is a measurement given in Celsius or Kelvin, used to measure how hot or cold something is.
• When water is heated, energy is transferred from the fuel's chemical store to the kinetic store of the water. This allows for the particles to vibrate and move quicker.
• The energy in a thermal store and temperature are not the same:

  • The energy of a thermal store is measured in Joules (J). It depends on the arrangement of the particles and how fast they are moving.
  • Temperature tells you about the average kinetic energy of particles.
• Heating can:

  • Change the energy stored within the system to increase the temperature.
  • Cause for a substance to change state.
  • Make chemical reactions.
• Physical changes are changes that do not produce new substances. Changes that do form new substances are called chemical changes.
• The specific heat capacity (J/kg $^{\circ}$C) is the energy required to raise one kg of a material by one degree Celsius.
• Heating increases the internal temperature of the material.
• The internal temperature is the energy that relates to the motion, vibration, rotation, and arrangement of the particles.
• Change in thermal energy (J) = Mass (kg) * Specific Heat Capacity (J/kg$^{\circ}$C) * change in temperature (∘C)
• Specific heat capacity tells you how resistant a material is to a change in temperature.
• Water is resistant to changes in temperatures, this makes it a good material for a central heating system. This is also why oceans are less likely to freeze.
• When ice is melted or when water boils, there is no temperature rise. The internal energy is increasing but the temperature does not. This is because the energy is transferred to break the attractive forces between water molecules.
• The specific latent heat of fusion (or melting) is the energy transferred when 1 kg of a substance changes from the solid to liquid state, or vice versa.
• The specific latent heat of vaporisation is the energy transferred when 1 kg of a substance changes from the liquid to gas state.
• Thermal energy for a change in state (J) = Mass (kg) * Specific Latent Heat (J/kg)
• Both specific latent heat and specific heat capacity involve energy changes for 1 kg of a substance, but latent heat is about the change of state, and heat capacity is about the change in temperature.