Melting

• Melting is when a solid changes into a liquid

• Requires heat energy which transforms into kinetic energy, allowing the particles to move

• Occurs at a specific temperature known as the melting point

Boiling

• Boiling is when a liquid changes into a gas

• Requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and within the liquid

• Occurs at a specific temperature known as the boiling point

Freezing

• Freezing is when a liquid changes into a solid

• This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same. Water, for example, freezes and melts at 0 ºC

• Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature 

Evaporation

• Evaporation occurs when a liquid changes into a gas and occurs over a range of temperatures

• Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid's surface at low temperatures, below the . of the liquid

• The larger the surface area and the warmer the liquid surface, the more quickly a liquid can evaporate

Condensation

• Condensation occurs when a gas changes into a liquid on cooling and it takes place over a range of temperatures

• When a gas is cooled its particles lose energy and when they bump into each other they lack the energy to bounce away again, instead they group together to form a liquid

Sublimation

• Sublimation occurs when a solid changes directly into a gas

• This only happens to a few solids, such as iodine or solid carbon dioxide

• The reverse reaction also happens and is called desublimation or deposition