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what is dulong-petit law?

Asked by disa.mahata 1st June 2017, 11:21 AM
Answered by Expert
Answer:
In 1819, shortly after Dalton had introduced the concept of atomic weight in 1808, Dulong and Petit observed that if they measured the specific heat per unit mass of a variety of solids, and divided by the atomic weights of those solids, the resulting per-atom specific heat was essentially constant.

The specific heat of copper is 0.093 cal/gm K (0.389 J/gm K) while that of lead is only 0.031 cal/gm K(0.13 J/gm K).  The difference is primarily because it is expressed as energy per unit mass. If it is expressed as energy per mole, they are very similar.

It is in fact that similarity of the molar specific heats of metals which is the subject of the Law of Dulong and Petit.

This is the Dulong-Petit law, although we have since given a name to that constant, which is 3R or 3kB, depending on whether the relative atomic mass (atomic weight) or the absolute atomic mass is used.

The similarity can be accounted for by applying equipatition energy to the atoms of the solids.

This law isn't precisely true, and isn't always true, and is never true at low temperatures. But it captures some physics that is equipartition theorem.

Dulong-Petit's law as: 

Energy per mole: 3kTNA 

k = Boltzmann constant

T = Temperature in kelvin

NA  = Avogadro's number

Dulong and Petit law:

Cv equals fraction numerator partial differential over denominator partial differential straight T end fraction left parenthesis 3 kTN subscript straight A right parenthesis space equals space 3 kN subscript straight A space per space mole space equals space 24.94 space straight J divided by mole space straight K
 

Answered by Expert 1st June 2017, 4:32 PM
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