P3

• in a solid :

  • particles are very close together
  • particles are arranged in a regular pattern
  • particles vibrate but do not move around
• in a liquid :

  • particles are close together
  • particles are not arranged in a regular pattern
  • particles can move around each other
• in a gas :

  • particles are spread out
  • particles are not arranged in any pattern
  • particles move around rapidly
• the density of a material tells us the mass for a given volume
• density = mass / volume

  p = m / v
• solids usually have a very high density because the particles are packed closely together, solids have a lot of mass for their volume
• solids usually have a very high density because the particles are packed closely together, solids have a lot of mass for their volume
• liquids have a high density because because the particles are close together, liquids have a lot of mass for their volume
• gases have a low density because the particles are very far apart so gases only have a small mass for their volume
• there are some exceptions to these such as :

  • polystyrene is a solid but it has a low density because it has a very open structure and is full of air spaces, so it has a small mass for its volume
• solids are extremely hard to compress which means squeeze because the particles in the solid are packed together in a regular pattern with almost no spaces between the particles
• solids have a fixed shape and they cannot move from place to place because in a solid, the particles can vibrate but they cannot move
• liquids are hard to compress because the particles are close together with not many spaces between them, unlike solids, liquids take the shape of their container and they can flow from place to place and that is because the particles in a liquid can move
• • gases can be easily compressed because the particles are widely spaced
  • gases spread out and fill the shape of their container because the particles in a gas move quickly and randomly
• we can change the state of a substance by putting in or taking out energy
• if we heat a solid, it can change state to a liquid and this is called melting
• in a liquid, the particles are moving around so they've got more kinetic energy than the particles in a solid. This means that we have to put energy in to convert a solid into a liquid. This energy is needed to break the forces of attraction between the particles in solid. Once those forces of attraction are broken, the particles can now move around
• the stronger the forces of attraction between the particles, the more energy we have to put in to break these forces and the higher the melting point
• if we cool a liquid, we can covert it back to a solid and this is called freezing
• when a substance freezes, the forces of attraction between the particles reform
• if we heat a liquid, we can convert it to a gas and this is called boiling
• if there are strong forces of attraction between the particles then the boiling point will be high and that is because it takes a lot of energy to break those strong forces of attraction and boil the liquid
• if we take a gas and cool it down then we can covert it back to a liquid and this is called condensation
• when a substance condenses, the forces of attraction between the particles reform
• the limitations of the particle model:

  • it assumes that all particles are spheres but this is not the case because particles have different shapes
  • it assumes there are no forces between the particles however the forces of attraction between the particles have a major impact on the melting and boiling points of a substance
• internal energy is the energy stored in a system by the particles
• internal energy is the total kinetic energy and potential energy of all the particles
• • if we heat a solid, we increase the internal energy. At some point, the solid can turn into a liquid by melting
  • if we continue to heat the liquid, again we continue increase the internal energy. At some point, the liquid will turn to a gas by boiling
  • if we cool the gas, then we reduce the internal energy. The gas turns to liquid by condensation
  • if we cool the liquid, then we reduce the internal energy even more. Liquid turns to solid by freezing
• a solid can turn directly into a gas and this is called sublimation
• when changes of state take place, mass is always conserved. We're not adding or taking away any particles
• changes of state are physical changes not chemical changes. If we reverse the change, the material recovers its original properties
• the specific heat capacity of a substance is the amount of energy required to raise the temperature of 1Kg of the substance by 1 degrees
• • when we heat a substance, we increase the temperature as we increase the energy of the particles
  • however, when the substance changes state e.g. melts, the temperature stops increasing and stays constant
  • now the energy that we are putting in is weakening or breaking the forces of attraction between the particles
• the specific latent heat of a substance is the amount of energy requires to change the state of 1kg of the substance with no change in temperature
• it takes 334000 J of energy to melt 1kg of ice and this is called specific latent heat of fusion
• the specific latent heat of a fusion is the energy required to change 1kg of a substance from a solid to a liquid with no change in temperature
• specific latent heat of vaporisation is the energy required to change 1kg of a substance from a liquid to a vapour with no change in temperature
• energy for a change of state = mass x specific latent heat
• • the pressure of a gas is due to the particles colliding with the walls of the container that the gas is held in
  • by colliding with the walls of the container, the gas particles are exerting a pressure
• we can increase the pressure if we increase the number of collisions per second or if we increase the energy of each collision