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Reference.org
Dulong–Petit law
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<p>The Dulong–Petit law, a thermodynamic law proposed by French physicists <a href="/facts/Pierre_Louis_Dulong/VDvEUtas">Pierre Louis Dulong</a> and <a href="/facts/Alexis_Th%25C3%25A9r%25C3%25A8se_Petit/djyRvptx">Alexis Thérèse Petit</a>, states that the classical expression for the molar <a href="/facts/Specific_heat_capacity/9P0U6YgI">specific heat capacity</a> of certain chemical elements is constant for temperatures far from the <a href="/facts/Absolute_zero/U3UyPl2K">absolute zero</a>. </p><p>In modern terms, Dulong and Petit found that the heat capacity of a <a href="/facts/Mole_(unit)/kCMFwCc0">mole</a> of many solid elements is about 3<i>R</i>, where <i>R</i> is the universal <a href="/facts/Gas_constant/RUXszrMH">gas constant</a>. The modern theory of the heat capacity of solids states that it is due to <a href="/facts/Phonon/tflWW6vw">lattice vibrations</a> in the solid. </p>