Dulong–Petit law for molar heat capacity of many solids at high temperature

E287399

The Dulong–Petit law states that many crystalline solids have an approximately constant molar heat capacity of about 3R at sufficiently high temperatures, reflecting classical equipartition of energy among atomic vibrations.

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Predicate Object
instanceOf empirical law
law of solid-state physics
thermodynamic law
appliesTo many crystalline solids
monatomic crystalline solids
approachedAsLimit high-temperature limit of the Debye model
high-temperature limit of the Einstein model
assumes classical behavior of atomic vibrations
each atom in a solid has three translational degrees of freedom
each vibrational degree of freedom contributes kB to energy per atom
harmonic approximation for atomic vibrations
basedOn equipartition theorem
surface form: classical equipartition theorem
concerns heat capacity of solids
lattice vibrations
explains approximate constancy of molar heat capacity of many solids at high temperature
failsAt low temperatures
field solid-state physics
statistical mechanics
thermodynamics
historicalContext formulated in the early 19th century
holdsBestFor heavy metallic elements
simple monatomic metals
impliesPerAtomHeatCapacity 3kB
involvesConstant Boltzmann constant
surface form: Boltzmann constant kB

universal gas constant R
isClassicalApproximationOf quantum theory of lattice vibrations
limitationsInclude deviations for covalent crystals like diamond
deviations for light-element solids
deviations for solids with low Debye temperature
mathematicalForm Cv,m ≈ 3R
molarHeatCapacityApproximateNumericalValue 24.9 J mol−1 K−1
25 J mol−1 K−1
molarHeatCapacityValue 3R
namedAfter Alexis Thérèse Petit
Pierre Louis Dulong
predicts constant molar heat capacity for many solids at high temperature
relatedConcept Debye model
surface form: Debye model of solids

Debye model
surface form: Einstein model of solids
relatesQuantity gas constant R
molar heat capacity at constant volume
states the molar heat capacity at constant volume is approximately 3R
temperatureRegime high temperature
usedFor estimating atomic weights of elements historically
usedIn introductory solid-state physics
introductory thermodynamics education
validWhen thermal energy kBT is large compared to vibrational quantum energies
yearProposed 1819

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equipartition theorem implies Dulong–Petit law for molar heat capacity of many solids at high temperature