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  Home > JCE Print > Journal of Chemical Education > Issues > 2006  > October  >
In the Classroom
Dulong and Petit's Law: We Should Not Ignore Its Importance
Mary Laing and Michael Laing
Durban 4001, Republic of South Africa
Cover
October 2006
Vol. 83 No. 10
p. 1499

Abstract
Dulong and Petit's law played an important role in the development of the periodic table as Mendeleyeff used this method in 1870 to correct the atomic weights of indium, cerium, and uranium that were wrong in the table of 1869. The discontinuous variation of molar heat capacity of a solid with change in temperature can be due to a phase change, order–disorder phenomena, or magnetic transitions. Two student exercises are described: the determination of the specific heat of a metal and hence its atomic weight (lab experiment) and a graphical study of specific heat versus atomic weight for different groups of metals and the confirmation of Dulong and Petit's law (classroom activity). The molar heat capacity is shown to be close to 26 J mol-1 K-1 for the solid elements. The anomalously low values for Be, B, C, and Si are explained by the Debye theory. The large value for Gd is shown to be a result of its magnetic properties; its Curie temperature is close to room temperature. The exercises are suitable for the general chemistry course.
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The laboratory experiment, the classroom activity, and notes for the instructor are available.
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Citation
Laing, Mary; Laing, Michael. J. Chem. Educ. 2006 83 1499.
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Keywords
Calorimetry / Thermochemistry; First-Year Undergraduate / General; Hands-On Learning / Manipulatives; Heat Capacity; History / Philosophy; Inorganic Chemistry; Inquiry-Based / Discovery Learning; Laboratory Instruction; Metals; Periodicity / Periodic Table
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History
Created:
Last Updated:
8/23/2006
8/30/2006
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Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations.
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