States of Matter

• Melting


  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 (m.p.)
• Boiling


  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 (b.p.)
• Freezing


  A liquid changes into a solid, the reverse of melting and occurs at exactly the same temperature as melting, requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature
• Evaporation


  A liquid changes into a gas and occurs over a range of temperatures, occurs only at the surface of liquids where high energy particles can escape from the liquid's surface at low temperatures, below the b.p. of the liquid, the larger the surface area and the warmer the liquid surface, the more quickly a liquid can evaporate
• Condensation


  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


  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
• Sublimation is no longer part of the syllabus, but you can see how it fits in on the interconversion diagram with the other state changes
• Kinetic theory of matter


  When substances are heated, the particles absorb thermal energy which is converted into kinetic energy, heating a solid causes its particles to vibrate more and as the temperature increases, they vibrate so much that the solid expands until the structure breaks and the solid melts, on further heating, the now liquid substance expands more and some particles at the surface gain sufficient energy to overcome the intermolecular forces and evaporate, when the b.p. temperature is reached, all the particles gain enough energy to escape and the liquids boils
• Heating curve


  A graph used to show how changes in temperature affect changes of state, the horizontal sections occur when there is a change of state but there is no change in temperature
• Cooling curve


  Like a heating curve, but is the mirror image