particle model of matter

Cards (34)

  • density (kg/m3) = mass (kg)/ volume (m3)
  • density is the mass per unit volume (how closely packed the particles are per unit volume)
  • the particle model can be used to explain the different states of matter and differences in density
  • model of solids --
    • particles closely packed
    • in a regular, structural arrangement
    • and particles vibrate about in fixed positions
    • solids have a definite shape (are rigid)
    • and a definite volume
    • cannot be compressed
  • model of liquids --
    • particles are closely packed
    • but have no regular arrangement
    • particles can slide past each other
    • liquids have no definitive shape - they can flow and take the shape of the container
    • but have a definite volume
    • cannot be compressed
  • model of gases --
    • particles are far apart
    • and particles move randomly and rapidly
    • gases have no fixed shape or volume
    • gases can be compressed because there are large gaps between particles, so it is possible to push the particles closer together unlike in a liquid and solid.
  • particles in a solid have low energy
    particles in a liquid have a greater energy
    particles in a gas have the highest energy
  • solids and liquids have similar densities (solids are a little more dense) because in them both, the particles are closely packed together. In a liquid, the particles have enough energy to push past each other, which isn't true for solids
  • gases have have far lower densities than solids and liquids as the spacing between atoms increases ten times, because the particles have lots of energy to move, so volume increases greatly and therefore density decreases (density = mass / volume)
  • mass is conserved during a change of state because the number of molecules in the substance undergoing a change of state doesn't change, meaning its mass does not change
  • in a change of state, reversible physical changes take place. No chemical changes take place because the material retains its original properties when reversed.
  • internal energy is the total energy (total kinetic and potential energy) stored inside a system by the particles that make up the system.
  • heating changes the energy stored within a system by increasing the energy of the particles that make up the system. This either raises the temperature of the system or produces a change of state
  • the specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of that substance by one degree celsius
  • change in thermal energy = mass X change in temperature X specific heat capacity
  • if the temperature of a system increases, the increase in temperature depends on:
    • the mass of the substance heated
    • the type of material
    • the energy input into the system
  • the specific latent heat of a substance is the amount of energy required to change the state of one kg of the substance with no change in temperature
  • when a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature
  • energy for a change of state = mass X specific latent heat
  • the molecules of a gas are in constant random motion
  • specific latent heat of fusion is the energy required to change 1kg of a substance from solid state to liquid state without a change in temperature
  • specific latent heat of vaporisation is the energy required to change 1kg of a substance from liquid state to gas state without a change in temperature
  • the temperature of a gas is related to the average kinetic energy of the particles in the gas
  • the motion of molecules in a gas changes according to the temperature and pressure of the gas
    • at a higher temperature, particles in a gas have higher kinetic energy as the two are related
    • this means the average speed of the particles increases leading to more frequent collisions at a higher energy
    • this means a greater force is exerted on the walls of the container leading to a higher pressure
    • therefore changing the temperature of a gas (held at a constant volume) changes the pressure exerted by the gas
  • the pressure of a gas is due to the particles of the gas colliding with the walls of the container that the gas is held in
  • the pressure in a gas produces a net force at right angles to the walls of the container
    • if you take a gas and increase the volume of the container (temperature constant), the pressure is reduced h
    • this is because the particles have a much greater space between them and the walls so have to ravel further before colliding with the walls of the container
    • this reduces the number of collisions per second between the particles and the walls, reducing the pressure
  • the pressure of a gas is inversely proportional to the volume. If one increases the other decreases.
  • for a fixed mass of gas held at a constant temperature, pressure x volume = constant
  • work is the transfer of energy by force
  • doing work on a gas increases the internal energy of the gas and can cause an increase in the temperature of the gas
  • gas particles colliding with the walls of the container apply a force at right angles to the walls of the container, and this causes gas pressure
    • during compression, a force is used to push a piston
    • work has now been done on the gas
    • because a force has been applied to the gas, energy has been transferred to the gas particles
    • this means the internal energy of the gas particles has increased
    • the temperature of the gas is related to the kinetic energy of the particles
    • internal energy = kinetic and potential energy
    • this means the kinetic energy of the gas has increased, so the temperature has increased because the two are related