ABSTRACT

A thermodynamic investigation of five alkali-metal uranyl molybdates of the general formula - A2[(UO2)(MoO4)2], where A = Li, Na, K, Rb, and Cs, was undertaken. The various phases were synthesized by solid-state reaction of ANO3, with A = Li, Na, K, Rb, or Cs, MoO3 and c-UO3. The synthetic products were characterized by X-ray powder diffraction and X-ray fluorescence methods. The low-temperature heat capacity, Cp , was measured using adiabatic calorimetry from T = (6 to 335) K. Based on these data, the third law entropy at T = 298.15 K, S , is (345 +- 1) J K 1 mol 1 for Li2[(UO2)(MoO4)2], (373 +- 1) J K 1 mol 1 for Na2[(UO2)(MoO4)2], (390 +- 1) J K 1 mol 1 for K2[(UO2)(MoO4)2], (377 +- 1) J K 1 mol 1 for Rb2[(UO2)(MoO4)2] and (394 +- 1) J K 1 mol 1 for Cs2[(UO2)(MoO4)2]. The enthalpy of formation of Li2[(UO2)(MoO4)2] was determined using HF solution calorimetry giving DfH (T = 298 K, Li2[(UO2)- (MoO4)2], cr) = (3456 +- 9) kJ mol 1. Using these new experimental results, together with literature data, the Gibbs free energy of formation of each compound was calculated, giving: DfG (T = 298 K, Li2[(UO2)(MoO4)2], cr) = (3204 +- 9) kJ mol 1, DfG (T = 298 K, Na2[(UO2)(MoO4)2], cr) = (3243 +- 2) kJ mol 1, DfG (T = 298 K, K2[(UO2)(MoO4)2], cr) = (3269 +- 3) kJ mol 1, DfG (T = 298 K, Rb2[(UO2)(MoO4)2], cr) = (3262 +- 3) kJ mol 1, and DfG (T = 298 K, Cs2[(UO2)(MoO4)2], cr) = (3259 +- 3) kJ mol 1. Smoothed Cp (T) values between T = (0 and 320) K are presented along with values for S and the functions [H (T) H (0)] and [G (T) H (0)]. DfS, DfH, and DfG behaviour at T = 298 K of the A2[(UO2)(MoO4)2] group is analysed as a function of the molar volumes of the different phases. The phase relations of K2[(UO2)(MoO4)2 in aqueous solution, in the presence and absent of carbon dioxide at T = 298 K, were studied by thermodynamic model calculations.

Compounds

#	Formula	Name
1	Li	lithium
2	Mo	molybdenum
3	U	uranium
4	O2	oxygen
5	Li2Mo2O10U	lithium uranyl molybdate (Li2[(UO2)(MoO4)2])
6	Mo2Na2O10U	sodium uranyl molybdate (Na2[(UO2)(MoO4)2])
7	K2Mo2O10U	potassium uranyl molybdate (K2[(UO2)(MoO4)2])
8	Mo2O10Rb2U	rubidium uranyl molybdate (Rb2[(UO2)(MoO4)2])
9	Cs2Mo2O10U	cesium uranyl molybdate (Cs2[(UO2)(MoO4)2])

Datasets

The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type	Compound-#	Property	Variable	Constraint	Phase	Method	#Points
POMD	5	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	5	Molar enthalpy, kJ/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	5	Molar entropy, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	5	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	140
POMD	6	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	6	Molar enthalpy, kJ/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	6	Molar entropy, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	6	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	140
POMD	7	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	7	Molar enthalpy, kJ/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	7	Molar entropy, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	7	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	134
POMD	8	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	8	Molar enthalpy, kJ/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	8	Molar entropy, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	8	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	153
POMD	9	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	9	Molar enthalpy, kJ/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	9	Molar entropy, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	18
POMD	9	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small (less than 1 g) adiabatic calorimetry	160
RXND	1 2 3 5 4	Molar enthalpy of reaction, kJ/mol				Solution calorimetry	1

Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

Thermodynamic properties and behaviour of A2[(UO2)(MoO4)2] compounds with A = Li, Na, K, Rb, and Cs

Lelet, M. I.[Maxim I.], Suleimanov, E. V.[Evgeny V.], Golubev, A. V.[Aleksey V.], Geiger, C. A.[Charles A.], Depmeier, W.[Wulf], Bosbach, D.[Dirk], Alekseev, E. V.[Evgeny V.]

ABSTRACT