Solids, Liquids & Gases (DP IB Physics: HL)

• The three states of matter are solid, liquid and gas
• The kinetic theory of matter is a model that attempts to explain the properties of the three states of matter
  • In this model, particles are assumed to be small solid spheres

Water has three states of matter; solid ice, liquid water and gaseous steam. The difference between each state is the arrangement of the particles

Solids

• Particles in solids:
  • Are held together by strong intermolecular forces
  • Are closely packed
  • Are arranged in a fixed pattern (lattice structure)
  • Can only vibrate about their fixed positions
  • Have low energies compared to particles in liquids and gases

In a solid, particles are arranged in a fixed pattern, with no spaces between them, and are only able to vibrate about their fixed positions

• As a result of the arrangement and behaviour of their particles, solids:
  • Have a fixed shape (although some solids can be deformed when forces are applied)
  • Have a fixed volume
  • Are very difficult to compress
  • Have higher densities than liquids and gases

Liquids

• Particles in liquids:
  • Are held together by weaker intermolecular forces compared to the forces between particles in solids
  • Are closely packed
  • Are randomly arranged (i.e. there is no fixed pattern)
  • Can flow past each other
  • Have higher energies than particles in solids, but lower energies than gas particles

In a liquid, particles are arranged randomly and are able to flow past one another

• As a result of the arrangement and behaviour of their particles, liquids:
  • Do not have a fixed shape and take the shape of the container they are held in
  • Have a fixed volume
  • Are difficult to compress
  • Have lower densities than solids, but higher densities than gases

Gases

• Particles in gases:
  • Have negligible intermolecular forces between them
  • Are far apart (the average distance between the particles is ∼10 times greater than the distance between the particles in solids and liquids)
  • Are randomly arranged
  • Move around in all directions at a variety of speeds, occasionally colliding with each other and with the walls of the container they are in
  • Are negligible in size compared to the volume occupied by the gas
  • Have higher energies than particles in solids and liquids

In a gas, particles can move around freely in all directions (shown by the arrows).

• As a result of the arrangement and behaviour of their particles, gases:
  • Do not have a fixed shape and take the shape of the container they are held in
  • Do not have a fixed volume and expand to completely fill the available volume
  • Can be compressed
  • Have the lowest densities (∼1000 times smaller than the densities of solids and liquids)

Step 1: Recall the equation for density 

Step 2: Write down the relationship between the density of a gas ρ_gas and the density of a liquid ρ_liquid

Step 3: Substitute into the density equation to show the relationship between the masses and volumes of a liquid a gas

Step 4: Since the mass stays the same, the relationship between the densities translates into a relationship between volumes as mass cancels out

Step 4: Relate the volume to the average distance between the molecules, x

• • The average distance x between the molecules is related to the cube root of the volume