IB Physics SL

Revision Notes

3.1.1 Solids, Liquids & Gases

Solids, Liquids & Gases

  • 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

 

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

 

  • 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

 

  • 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

gas-density, IGCSE & GCSE Physics revision notes

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)

 

Worked Example

Liquids are about 1000 times denser than gases. Let d be the diameter of a molecule. Estimate the average intermolecular distance in a gas. Give your answer in terms of d

Step 1: Recall the equation for density 

ρ = m / V

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

ρliquid = 1000 ρgas

Step 3: Write down the relationship between the volume of a liquid and the volume of a gas

      • since the mass stays the same, the relationship between the densities translates into a relationship between volumes

    Vliquid = 1000 Vgas

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

    x = ∛1000 Vliquid = 10d

Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top