IB DP Physics: SL复习笔记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

3.1.1-Diagram-1-States-of-Matter

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

3.1.1-Diagram-2-Solids

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

3.1.1-Diagram-2-Liquids

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

gas-density

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)

3.1.1-Diagram-3-Table

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

Density-Equation_2

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

ρliquid = 1000 ρgas

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

    • 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

 

 

 

 

 

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