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Why about 1 kJ/kg/K for so many solids?

  1. Apr 29, 2009 #1
    Most solid components I need to consider at work have a specific heat of about 1 kJ/kg/K.
    Why is that so?
    Any explanation as simple as for perfect gases?

    Thanks
     
  2. jcsd
  3. Apr 29, 2009 #2
    Yes, it's mode-counting, similar to perfect gasses. Counting the vibrational modes of each atom in the lattice it's 3/2 kT for the kinetic modes and another 3/2 kT for the potential energies.
     
  4. Apr 30, 2009 #3
    Thanks conway.

    One of the solids in my long list is 3(CaO).SiO2 and another is 3(CaO)(MgO)2(SiO2).
    This would mean that "heavier" molecules are not very rigid, therefore making room for more modes and more specific heat per molecule. The end result around 1 kJ/kg/K depends also on the atoms involved.
     
  5. Apr 30, 2009 #4

    Vanadium 50

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    This makes more sense when you express it as 25 J/mol/K. Most solids have that as their specific heat. This is called the Law of Dulong and Petit. It works for exactly the reason Conway said.
     
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