Physics density

• Density


  Mass per unit volume
• Density


  • Depends on the spacing of the atoms in matter
  • Solids and liquids have similar densities as the space between particles does not change significantly
  • Liquids usually have a lower density than solids (main exception is ice and water)
  • Gases have a far lower density as the spacing between atoms increase x10, as the particles have lots of energy to move, so volume increases greatly and therefore the density decreases greatly compared to solids/liquids
• If questions involve change in state and ask for new volume/pressure, the mass is the same!
• Changes of state


  • Mass is conserved during a change of state
  • Physical changes are reversible, and not chemical changes
  • They are not chemical because the material retains its original properties when reversed
• Changes of state


  1. Melting

  2. Evaporating

  3. Freezing

  4. Condensing

  5. Sublimation
• Internal energy


  Energy which is stored by particles (atoms and molecules) within a system, in the forms of kinetic energy and potential energy
• Heating a system


  Increases the energy the particles have, which either raises the temperature of the system or produces a change of state
• Specific heat capacity


  The amount of energy required to raise the temperature of 1kg of a substance by 1°C
• Specific latent heat


  The amount of energy needed to change the state of 1kg of a substance without a change in temperature
• Energy is absorbed when melting and evaporating and energy is released when freezing and condensing
• Sublimation is when solid goes straight to gas - "dry ice" (solid CO2 does this)
• Pressure


  The total force exerted by all of the molecules inside the container on a unit area of the walls
• Changing the temperature of a gas, held at constant volume


  Changes the pressure exerted by the gas (Pressure law)
• Changing the volume of a gas


  Affects the pressure (Boyle's law)
• Increasing the pressure of a gas

  Doing work on a gas increases its temperature
• Adding more particles to a fixed volume

  Increases the pressure and temperature of the gas
• A fixed number of particles in a smaller volume

  Increases the pressure and temperature of the gas
• States of Matter


  • Solids
  • Liquids
  • Gases
• Density


  Mass per unit volume
• Density formula


  ρ = m/v
• Density is measured in kg/m³
• Mass is always conserved in changes of state
• Changes of State


  1. Melting: Solid → Liquid

  2. Evaporation: Liquid → Gas

  3. Condensation: Gas → Liquid

  4. Sublimation: Solid → Gas
• Internal Energy


  The total kinetic and potential energies of the particles in a system
• Solids


  • Particles can only vibrate about fixed positions
• Liquids


  • Particles can flow over each other
• Gases


  • Particles can move freely
• Density


  Solids have the highest density, gases have the lowest density
• Kinetic Energy


  Solids have the least kinetic energy, gases have the most kinetic energy
• Physical Changes


  If change is reversed the material's properties can be recovered
• Chemical Changes


  Cannot easily recover its original properties
• Changes of state are physical changes
• When a solid changes to a gas without becoming a liquid, this is called sublimation
• Particle Motion


  Molecules are in constant random motion
• Pressure


  Pressure in gases produces a force at right angles to the container it is in
• Temperature


  Temperature is determined by the kinetic energy of the substance, the higher the temperature the higher the kinetic energy
• Specific Heat Capacity


  The energy required to raise the temperature of 1kg of a substance by 1°C
• Specific Latent Heat


  The energy required to change the state of 1kg of a substance without a change in temperature
• Latent Heat of Fusion

  The energy required to change a substance from solid to liquid
• Latent Heat of Vaporisation

  The energy required to change a substance from liquid to vapour