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 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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- 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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