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Thermal Properties of Matter


8. Calorimetery


  • Calorimetery means measurement of Heat.
  • Calorimeter is the device used to measure heat and it is cylinderical vessel made of copper and provided by a stirrer and a lid.
  • This vessel is kept in a wooden block to isolate it thermally from suroundings.A theromometer is used to measure the temperature of the content in the calorimeter.
  • When bodies at diffrent temperature are mixed in a calorimeter,they exchange heat with each other.
  • Bodies at higher temperature loose heat while bodies at low temperature gain heat.Contents of the calorimeter is continously stirred to keep temperature of contents uniform
  • Thus principle of calorimetery states that the total heat given by hot objects is equal to the total heat received by cold objects.



9.Change of phases:


  • There are three phases of matter i.e, Solid, Liquid and Gas.
  • Substance for example, H2O exists in solid phase as Ice,in liquid phase as Water and in gas state as Steam.
  • Transtion from one phase to another phase are accompained by absorption or liberation of heat and usually by change in volume even at constant T.
  • Change of phase from solid to liquid is called melting , from liquid to solid is called fusion and from liquid to gas is called vaporisation
  • Once the temperature for phase change is reached( e,g melting or boiling temperature) no further temperature change occurs until all the substance has undergone phase change.

    Melting Point:-Temperature at which solid and liquid phase are in thermal equilibrium with each other
    Boiling point:-Temperature at which liquid and vapour phase are in thermal equilibrium with each other

  • Change of phase from solid state to Vapour state without passing through liquid state is called sublimation for e.g Dry Ice and Iodine sublimes.

10. Latent Heat:
  • The amount of heat per unit mass that must be transfered as heat when a sample completely undergoes phase change is called latent Heat of the substance for the process.
  • Thus when a sample of mass m completely undergoes phase change,the total energy transfered is
    Q=Lm
    where,
    L- Latent heat and is characterstics of a substance
  • Its unit is JKg-1.
  • Latent Heat for a solid liquid change is called Latent Heat of Fusion Lf.
  • Latent Heat for a liquid gas change is called Latent Heat of Vaporisation Lv.




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