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Low-Temperature Heat Capacities and High-Temperature Enthalpies of Sodium Chromate.

PB213876

Publication Date	1972
Personal Author	Ferrante, M. J.; Stuve, J. M.; Krug, M. P.
Page Count	18
Abstract	Low-temperature heat capacities and high-temperature enthalpies were determined calorimetrically for Na2Cr04. A reversible transition was found at 700K with an isothermal heat of transition of 2,263 cal/mole. High-temperature X-ray diffraction analysis showed that the transition was a crystal change from the low-temperature orthorhombic form to the high-temperature hexagonal form. Powder diffraction data for the high-temperature form are given and possible structures discussed. The melting point was determined to be 1,065K with a heat of fusion of 5,810 cal/mole. Enthalpy and entropy increments from the investigation were combined with other data from the literature to calculate enthalpies of formation, free energies of formation, and equilibrium constants of formation from 298 to 1,400K. Equations representing enthalpies above 298K are given. (Author)
Keywords	Chromates Thermodynamic properties Specific heat Enthalpy Sodium inorganic compounds X ray diffraction Crystal structure Sodium chromates
Source Agency	Invalid Source Agency Code
NTIS Subject Category	99F - Physical & Theoretical Chemistry
Corporate Authors	BUREAU OF Mines, Washington, D.C.
Supplemental Notes	Prepared in cooperation with Albany Metallurgy Research Center, Oreg.
Document Type	Technical Report
Title Note	Rept. of Investigation Jun 70-Jun 72.
NTIS Issue Number	197305

Low-Temperature Heat Capacities and High-Temperature Enthalpies of Sodium Chromate.

Low-Temperature Heat Capacities and High-Temperature Enthalpies of Sodium Chromate.
PB213876

Publication Date	1972
Personal Author	Ferrante, M. J.; Stuve, J. M.; Krug, M. P.
Page Count	18
Abstract	Low-temperature heat capacities and high-temperature enthalpies were determined calorimetrically for Na2Cr04. A reversible transition was found at 700K with an isothermal heat of transition of 2,263 cal/mole. High-temperature X-ray diffraction analysis showed that the transition was a crystal change from the low-temperature orthorhombic form to the high-temperature hexagonal form. Powder diffraction data for the high-temperature form are given and possible structures discussed. The melting point was determined to be 1,065K with a heat of fusion of 5,810 cal/mole. Enthalpy and entropy increments from the investigation were combined with other data from the literature to calculate enthalpies of formation, free energies of formation, and equilibrium constants of formation from 298 to 1,400K. Equations representing enthalpies above 298K are given. (Author)
Keywords	Chromates Thermodynamic properties Specific heat Enthalpy Sodium inorganic compounds X ray diffraction Crystal structure Sodium chromates
Source Agency	Invalid Source Agency Code
NTIS Subject Category	99F - Physical & Theoretical Chemistry
Corporate Authors	BUREAU OF Mines, Washington, D.C.
Supplemental Notes	Prepared in cooperation with Albany Metallurgy Research Center, Oreg.
Document Type	Technical Report
Title Note	Rept. of Investigation Jun 70-Jun 72.
NTIS Issue Number	197305