Changes of State (HL IB Chemistry)

What are the Three States of Matter?

Solids

• Solids have a fixed volume and shape and they have a high density
• The atoms vibrate in position but can’t change location
• The particles are packed very closely together in a fixed and regular pattern

Liquids

• Liquids also have a fixed volume but adopt the shape of the container
• They are generally less dense than solids (an exception is water), but much denser than gases
• The particles move and slide past each other which is why liquids adopt the shape of the container and also why they are able to flow freely

Gases

• Gases do not have a fixed volume, and, like liquids, take up the shape of the container, but they fill the whole container
• Gases have a very low density
• Since there is a lot of space between the particles, gases can be compressed into a much smaller volume
• The particles are far apart and move randomly and quickly (around 500 m/s) in all directions
• They collide with each other and with the sides of the container (this is how pressure is created inside a can of gas)

Particle Arrangements in the Three States of Matter

State	Solid	Liquid	Gas
Density	High	Medium	Low
Arrangement of particles	Regular pattern	Randomly arranged	Randomly arranged
Movement of particles	Vibrate around a fixed position	Move around each other	Move quickly in all directions
Energy of particles	Low energy	Greater energy	Highest energy
2D Diagram

               

• Changes of state are physical changes that are reversible
• These changes do not change the chemical properties or chemical makeup of the substances involved
• Vaporisation includes evaporation and boiling
• Evaporation involves the change of liquid to gas, but unlike boiling, evaporation occurs only at the surface and takes place at temperatures below the boiling point
• Boiling occurs at a specific temperature and takes place when the vapour pressure reaches the external atmospheric pressure

Changes of State Diagram

State changes and their interconversions can be represented using particle diagrams which help to emphasise the spacing and order of the particles. Energy is increasing left to right across this diagram

• When writing and balancing chemical equations sometimes it is necessary to represent the physical states of substances using the four state symbols
• In exams it is usually indicated where marks are awarded for this
• State symbols are essential in equations that represent defined thermodynamic conditions such as equations for ionisation energy, lattice enthalpy and enthalpy of formation