Science GCSE (B1,C1,P1) Physics

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Moving and storing heat - Heat

  • Heat is a measure of energy
  • When a substance is heated, it gains kinetic energy. This means the particles in the gas/liquid move around quicker and in solids they vibrate more. 
  • This is what makes them boil and melt.
  • Heat is measured on an absolute scale, this means it cannot go below zero because there is a limit to how slow particles can move/vibrate.
  • Unit of heat energy is joules (J)
  • The heat travels from hot to cold. 
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Temperature

  • Temperature is a measure of the average kinetic energy of the particles in a substance. The hotter something is, the higher the temperature and therefore the higher Kinetic energy of its particles.
  • Not absolute scales as they can go below zero.
  • If there's a difference between two objects temperature, energy will flow between them.
  • The greater the difference in temperature, the faster the rate of cooling.
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Specific heat capacity

  • How much energy stuff can store in a given amount.
  • Some materials take more energy to heat up than others.
  • How much energy needed to raise 1kg of a substance by 1'C.
  • For example, water, its SHC is high, once it's heated it can store lots of energy which makes it good for central heating. 
  • EQUATION:   Energy= Mass x SHC X Temperature change
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Intermolecular Bonds

  • You need to put energy in to break intermolecular bonds.
  • When you heat a liquid, the particles move faster. Eventually when enough of the particles have enough energy to break the attraction to each other, bug bubbles of gas form in the liquid (boiling).
  • Similar in solids - Heat them enough and eventually the particles break up and it melts.
  • When a substance is melting or boiling it is using the input energy for breaking the bonds instead of raising the temperature. So you get flat points on the graphs.
  • When a substance is condensing or freezing, bonds are forming between particles which releases energy. Temperature doesn't go down until all the substance has been turned into a solid or liquid.
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Specific Latent Heat

  • The amount of energy needed to change the state of a substance. 
  • The specific latent heat of melting is the amount of energy needed to melt 1kg of a substance without changing its temperature (material has to be at its melting point already)
  • The specific latent heat of boiling is the amount of energy needed to  boil 1kg of a substance without changing its temperature (material has to be at its boiling point already)
  • Different for all materials and different for melting and boiling.
  • EQUATION: Energy = Mass x Specific latent heat
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