molecules and matter

• Changes of state are physical changes because no new substances are produced.
• When the temperature of a substance is increased, the kinetic energy store of its particles increases and the particles vibrate or move faster.
• If the kinetic store of a substance’s particles increases or decreases enough, the substance may change state.
• Heating a substance increases its internal energy.
• Internal energy is the sum of the total kinetic energy the particles have due to their motion and the total potential energy the particles have due to their positions relative to each other
• The energy transferred when a substance changes state is called the latent heat.
• Specific latent heat – the energy required to change 1 kg of a substance with no change in temperature.
• Specific latent heat of fusion – the energy required to melt 1 kg of a substance with no change in temperature
• Specific latent heat of vaporisation – the energy required to evaporate 1kg of a substance with no change in temperature.
• The particles in a gas are constantly moving in random directions and with random speeds.
• The temperature of a gas is related to the average kinetic energy of its particles.
• When a gas is heated, the particles gain kinetic energy and move faster, so the temperature of the gas increases.
• The pressure a gas exerts on a surface, such as the walls of a container, is caused by the force of the gas particles hitting the surface.
• The pressure of a gas produces a net force at right angles to the walls of a container or any surface.
• Which two quantities do you need to measure to find the density of a solid or liquid?

  mass and volume
• Why is the mass of a substance conserved when it changes state?

  the number of particles does not change