internal energy and changes of state

• Internal energy


  The total amount of kinetic energy and chemical potential energy of all the particles in the system
• When energy is given to raise the temperature

  Particles speed up and gain kinetic energy
• When the substance melts or boils


  Energy is put in to breaking the bonds that are holding particles together, which increases the potential energy
• The conservation of energy means that, assuming no energy is lost to the environment, any energy transferred to a material will be distributed between the chemical store and the thermal store of the internal energy
• Whether the energy breaks bonds, increases the speed of the particles to stretch bonds, or just increases the speed of the particles depends on the temperature and state of the material
• Solid


  One of the three states of matter, where particles are closely packed and have a fixed shape and volume
• Liquid


  One of the three states of matter, where particles are close together but can move around, having a fixed volume but no fixed shape
• Gas


  One of the three states of matter, where particles are far apart and can move around freely, having no fixed shape or volume
• Particle model


  A model that explains the properties of substances in their different states, as well as changes of state
• Sublimation


  When a solid turns straight into a gas on heating, without becoming a liquid first - or when a gas turns straight into a solid, without becoming a liquid
• Solid carbon dioxide ('dry ice') can sublime
• Melting


  The process that occurs when a solid turns into a liquid when it is heated
• Evaporation


  The process in which a liquid changes state and turns into a gas
• Boiling


  Changing from the liquid to the gas state, in which bubbles of gas form throughout the liquid
• Energy must be transferred, by heating, to a substance for changes of state to happen</b>
• During changes of state, particles gain energy, which is used to break some of the bonds between particles and overcome the remaining forces of attraction between particles
• The stronger the forces between particles, the higher the melting and boiling points
• The strength of the forces between particles depends on the particles involved
• Bonding type


  • Ionic
  • Small molecules
• Evaporation can take place below the boiling point of a substance
• Condensing


  Energy is transferred from a substance to the surroundings when a substance condenses
• Freezing


  Energy is transferred from a substance to the surroundings when a substance freezes
• Predicting a physical state


  If melting point and boiling point are known, the state of a substance at a given temperature can be predicted
• The particle model assumes that particles are solid spheres with no forces between them
• Particles are not solid, since atoms are mostly empty space
• Many particles are not spherical
• Particle model


  Model that describes the arrangement, movement and energy of particles in a substance
• Particle model


  • Explains the properties of substances in their different states
  • Explains changes of state
• States of matter


  • Solids
  • Liquids
  • Gases
• Solids


  • Have a fixed shape and cannot flow
  • Cannot be compressed
• Liquids


  • Flow and take the shape of their container
  • Cannot be compressed
• Gases


  • Flow and completely fill their container
  • Can be compressed
• A single particle does not have the properties of the material it is part of
• The properties of a substance are the properties of a huge number of particles together