Particle Theory

• What is the formula for change in thermal energy?

  Change in Thermal Energy = mass × specific heat capacity × temperature change
• What happens to the properties of a substance during a chemical change?

  The substance does not usually restore its original properties when the changes are reversed.
• What is condensation?


  Condensation is the changing from vapour state to a liquid state when a substance is cooled.
• How is density defined?

  Density is the mass per unit volume of an object.
• What is evaporation?


  Evaporation is the changing from liquid state to a vapour state when a substance is heated.
• What occurs during freezing?

  Freezing is the changing from a liquid state to a solid state when a substance is cooled.
• How is gas temperature related to kinetic energy?

  The temperature of a gas is directly proportional to the average kinetic energy of its molecules.
• What is internal energy?

  Internal energy is the energy stored by the atoms and molecules that make up a system, equal to the sum of total kinetic and potential energies of the particles in the system.
• What is latent heat?

  Latent heat is the energy required for a substance to change state.
• What occurs during melting?

  Melting is the changing from solid state to liquid state when a substance is heated.
• What is the unit of pressure?

  Pascals is the unit of pressure, equal to a force of one Newton acting perpendicular to an area of one metre squared.
• What are physical changes?

  Physical changes are changes to the physical properties of a substance which can be reversed.
• How do changes of state relate to physical changes?

  Changes of state are physical changes since substances can restore their original properties when the changes are reversed.
• What is pressure defined as?

  Pressure is the force acting perpendicular to a surface, per unit area.
• What is specific heat capacity?

  Specific heat capacity is the amount of energy needed to increase the temperature of one kilogram of a given substance by one degree Celsius.
• What is specific latent heat of fusion?

  Specific latent heat of fusion is the amount of energy needed to change the state of one kilogram of a substance from solid state to liquid state, whilst held at constant temperature.
• What is specific latent heat of vaporisation?

  Specific latent heat of vaporisation is the amount of energy needed to change the state of one kilogram of a substance from liquid state to vapour state, whilst held at constant temperature.
• What is specific latent heat?

  Specific latent heat is the amount of energy needed to change the state of one kilogram of a substance, whilst held at constant temperature.
• What is sublimation?


  Sublimation is the direct changing of a substance from a solid state to a vapour state, without passing through the liquid phase.
• The particle theory states that all matter is made up of tiny particles that are constantly in motion.
• In a gas, particles are far apart and move freely at high speeds.
• In a solid, particles are closely packed together and vibrate in fixed positions.
• The kinetic theory states that particles have mass and occupy space (volume).
• Liquids also contain many small particles but they move more slowly than those found in gases.
• Pressure increases as more gas particles hit the walls of a container per unit time.