Edgar F. Westrum

The heat capacity of thorium dioxide was determined from 10 to 305°K in an adiabatic calorimeter. As expected, no anomaly was observed in the heat capacity. The enthalpy, entropy, and free energy were calculated from the heat-capacity data and are tabulated for several temperatures. At 298.16°K the entropy and the enthalpy are, respectively, 15.593±0.02 cal deg−1 mole−1 and 2524.4±3 cal mole−1. By assuming the lattice entropy of uranium dioxide and of neptunium dioxide to be equal to the entropy of thorium dioxide, the magnetic entropy contributions at 298.16°K were evaluated as 3.0 cal deg−1 mole−1 for uranium dioxide and 3.6 cal deg−1 mole−1 for neptunium dioxide. These values are somewhat greater than the spinonly values (R ln 3=2.18 cal deg−1 mole−1 for uranium dioxide and R ln 4=2.75 cal deg−1 mole−1 for neptunium dioxide). The entropies of the other isomorphous actinide dioxides at 298.16°K are estimated to be (in cal deg−1 mole−1) 17.8 for PaO2, 19.7 for PuO2, 20.0 for AmO2, 20.3 for CmO2, 20.6 for BkO2, and 20.3 for CfO2.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHEAT CAPACITIES AND THERMODYNAMIC PROPERTIES OF GLOBULAR MOLECULES. I. ADAMANTANE AND HEXAMETHYLENETETRAMINE1Shu-Sing Chang and Edgar F. Westrum Jr.Cite this: J. Phys. Chem. 1960, 64, 10, 1547–1551Publication Date (Print):October 1, 1960Publication History Published online1 May 2002Published inissue 1 October 1960https://pubs.acs.org/doi/10.1021/j100839a050https://doi.org/10.1021/j100839a050research-articleACS PublicationsRequest reuse permissionsArticle Views443Altmetric-Citations148LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

The heat capacity of a two-gram sample of neptunium dioxide was determined from 10 to 315°K in an adiabatic calorimeter. At 298.16°K the molal entropy and enthalpy calculated from the heat capacity data are 19.19±0.1 cal deg−1 and 2770±15 cal, respectively. A pronounced hump was found in the heat capacity curve of neptunium dioxide at 25.3°K similar to that found by Jones, Gordon, and Long in uranium dioxide at 28.7°K. This anomaly in the heat capacity is suggestive of a cooperative phenomenon and is attributed to the incidence of antiferromagnetism below the temperature of the maximum in the heat capacity. A calorimeter for gram scale samples and a modification of the cryostat design of Ruehrwein and Huffman so as to employ only liquid helium and liquid nitrogen as refrigerants are described.