Temperature change and energy

• Changes in a material's temperature or state of matter are caused by changes to the internal energy.
• The energy required by different materials depends on their 'heat capacity' and 'latent heat'.
• In everyday life, there are three states of matter: solid, liquid or gas.
• The differences between the three states are due to the arrangement and spacing of the particles and their motion.
• Solids, liquids and gases can be categorised based on the particles in them.
• The particles in a solid are in a regular arrangement, vibrate about a fixed position and sit very closely together.
• The particles in a liquid are randomly arranged, move around each other and sit close together.
• The particles in a gas are randomly arranged, move quickly in all directions and are far apart.
• Changing state in matter involves adding or removing energy from a material, which can cause it to change from one state to another.
• Heating a solid material will cause it to melt, the process that occurs when a solid turns into a liquid when it is heated.
• Continued heating will cause the liquid to boil or evaporate, when liquid is vaporised and turns to a gas.
• In some instances, a solid material can go straight to being a gas without first becoming a liquid when heated, a process called sublimation.
• Cooling a gas will cause it to condense, a change of state in which gas becomes liquid by cooling.
• Further cooling will cause the liquid to freeze, a change of state in which liquid becomes solid by cooling.
• Boiling is an active process, people actively apply energy to a liquid to turn it into a gas using a heater such as a kettle.
• Evaporation is a passive process, the liquid slowly absorbs energy from the surrounding area so that some of its particles gain enough energy to escape the liquid.
• These changes in state are called physical changes because the process can be reversed (eg by cooling instead of heating).
• This is different to the changes seen in a chemical reaction, which cannot be reversed so easily.