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Enthalpy of formation of europium monoxide
J. Chem. Thermodynamics 1969, 1,301-304
Enthalpy of formation monoxide? ELMER
J. HUBER,
of europium
Jr., and CHARLES
E. HOLLEY,
Jr.
University of California, Los Alamos Scientific Laboratory Los Alamos, New Mexico 87544, U.S.A. (Received I8 December 1968) The enthalpy of formation of europium monoxide (EuO~.~~) has been determined by means of oxygen bomb calorimetry and found to be A.HF(298.15 K, EuOl.& = - (143.3 4 0.5) kcal mol-l. A value of AHi(298.15 K, EuO) = - (135.0 * 1.3) kcal mol-’ was derived.
1. Introduction Little is known about the thermochemical properties of the lower oxides of the lanthanides. In fact, only EuO and Eu,O, are definitely known to exist. The compounds previously reported to be SmO and SmO,.,-,,, have been shown to be the nitride and hydride, respectively, and the existence of YbO must be considered doubtful.“) This paper reports the results obtained from the combustion of a sample of EuO in an oxygen bomb calorimeter. These results when combined with the enthalpy of formation of Eu,O,,(‘) yield the enthalpy of formation of EuO. The EuO was prepared by John Burnett (now of Oak Ridge National Laboratory) at the Lawrence Radiation Laboratory, University of California, Berkeley, in 1964 by the reaction of Eu with Eu,O,. Two separate batches of approximately equal quantity were made. The first analyzed as EuO~.~~~*~,~,,~, and the second as EuO~,,,~,-,~~,~~~. These determinations were made by Burnett by measuring the increase in mass upon oxidation. X-Ray analysis gave a = 5.1429 and 5.1428 A respectively for, these facecentered cubic materials. Twenty foreign metals were shown to be absent or present in amounts less than the limit of detection. The two samples were mixed prior to chemical analysis at Los Alamos and burning in the bomb. Chemical analyses gave H, 0.005 ; C, 0.0095; N, 0.020 mass per cent. Two samples were dissolved in 6 M hydrochloric acid solution, which had been distilled under vacuum, in the presence of platinum black. The volume of the gas evolved was measured and the percentage of hydrogen determined with a mass spectrograph. The platinum was used to catalyze the oxidation of Eu2+ by H+ and the production of the corresponding amount of hydrogen. An average value of EuO~.~~~*,,~,,~ was found for the composition of the monoxide which may indicate a slight oxidation during storage since the average of Burnett’s values is EuO,.,,,. The method involved the determination of the heat evolved from the combustion of a weighed sample of the europium monoxide at a known initial pressure of oxygen. t Work done under the auspices of the U.S. Atomic Energy Commission.
0 1 1 9
0.222 0.009 0.012 0.016
2.812 3.035 3.020 3.002
8 5 5 8
m(Eu0M.z (unburned)
m@uO)lg (burned) 31.1 11.2 17.2 17.2
TABLE
6.16 5.05 6.81 5.82
~OWmg wire)
(fuse
1. Energy of combustion
2 2 2 2
391.4 390.8 390.8 390.8
C/Cal K-1
of europium
1 0 0 1
AL&al
0.398 0.429 0.429 0.424
6.4 5.6 5.7 5.8 average : standard deviation of mean:
AT/K
monoxide
-323.3 -326.2 -324.3 -324.3 -324.5 0.6
AeJcal g-l
ENTHALPY
OF FORMATION
OF EUROPIUM
MONOXIDE
303
The method and equipment have been described. (3) Because of the limited amount of material available, only four runs were made. For the first run the combustion was carried out on discs of Eu,O, resting on a platinum stand. For the succeeding runs a platinum dish resting on a Eu,O, disk contained the coarse powder. The mass of platinum was 109.5 g in the first case and 122.1 g in the other three. The runs were made at 25 atm oxygen pressure. The energy equivalent C of the calorimeter was (2385.7kO.7) cal K-’ as determined with standard benzoic acid (NBS sample 39i). The calorie is the defined thermochemical calorie equal to 4.184 J. Temperature measurements were made with a platinum resistance thermometer and a Mueller bridge. Because of the possible reaction of the atmosphere with the oxide, the weighing of the material and loading of the bomb were carried out in a dry, inert-atmosphere box. When a sample of the material was subjected to 25 atm pressure of oxygen for one hour, a small (0.03 per cent) increase in mass was noted. A 0.01 in diameter magnesium fuse wire was used to ignite the samples. Its energy of combustion was taken as 5900 cal g-‘. The electrical energy required to ignite the fuse wire was measured with a current integrator. A microscopic examination of a combustion product showed no cubic phase of Eu,O, present. X-Ray analysis revealed only the monoclinic (B) form. Each combustion product was analyzed for completeness of combustion by dissolving in 6 M hydrochloric acid solution, as has been described above. The completeness of combustion thus determined was low for the first run (93 per cent) but high (> 99 per cent) for the next three runs.
2. Results Listed in table 1 are the results of the four runs. Shown in column (1) is the amount of sample burned after subtraction of the unburned material as listed in column (2). A,?& is the electrical energy used to ignite the fuse wire. The average, - 324.5 cal g-r, has a standard deviation of the mean of 0.6 cal g-‘. Corrections were applied for the impurities present. It was assumed that EuH,, EuC, and EuN were the contaminants which contributed to the energy of combustion in accordance with their enthalpies of formation and those of their combustion products. These enthalpies were taken to be A.H,“(EuH,) = -45 (estimated), AH,“(EuC) = -25 (estimated), AH,“(EuN) = -70 (estimated), AHF(C02) = -94,(4’ AHfO(H20,g) = -58,c4’ and AHf”(Eu,O,) = -393.9 kcal mol -’ .(‘) It was assumed that the nitride burned to nitrogen. The impurity correction reduced the magnitude of the combustion value by 2.06 per cent to - (317.8 f 1.8) cal g- ‘. The uncertainty given for the final value is twice the standard deviation of the mean combined with the uncertainty in the determination of the energy equivalent of the calorimeter and an estimated uncertainty for the impurity correction. Correction to unit fugacity of oxygen and to a constant pressure process leads to AH” = -(107.3 f0.6) kcal mol-’ for the reaction 2 Eu01,02(~)+0.48
O,(l atm) = Eu,O,(mono.)
The 1961 atomic weights were used. (‘) The A(PV) term amounted to 0.29 kcal mol-’ and the correction for non-ideality of oxygen to 0.04 kcal mol-‘.
304
The combination
E. J. HUBER,
JR. AND
C. E. HOLLEY,
JR.
3. Discussion of this reaction with 2 Eu(s)+ j- 02(1 atm) = Eu,O,(mono.); AH: = -(393.9+0.9) kcal mo1-1,(2)
yields AH~(Eu01.c2) = -(143.3 +0.5) kcal mol-‘. If the assumption is made that the EuO,,,, is a mixture of EuO and Eu,O,(mono.) then the material may be considered to be Eu0.0.021 Eu,O,. AH,“(EuO) may be calculated by taking AH,“(EuO) = { - 143.3 +0.5+(0.021+0.003)(393.9 +0.9)} kcal mol-‘, = -(135.0+1.3) kcal mol-‘, where the uncertainty now includes the uncertainty in the determination of the formula. Burnett and Cunningham (@ have reported AH,“(EuO) = - 145.2 kcal mol- ’ from enthalpies of solution of the metal and of EuO,.,, in HCl solutions. Haschke and Eick”’ have found AH,“(EuO) = -(145.2f4.1) kcal mole1 from an effusion method. The reason for the discrepancy is not apparent.
The authors thank John L. Burnett for preparing the samples of europium monoxide and supplying X-ray and spectroscopic analyses. They appreciate the work of Finley Ellinger, X-ray analysis of the combustion product, and of Carolyn MacDougall and Bert Baca, chemical analysis. REFERENCES 1. 2. 3. 4.
Felmlee, T. L. Thesis, Arizona State University. 1967. University Microfilm Order No. 67-7359. Huber, E. J., Jr.; Fitzgibbon, G. C.; Holley, C. E., Jr. J. Whys. Chem. 1964, 68, 2720. Holley, C. E., Jr.; Huber, E. J., Jr. Los Alamos Scientific Laboratory Rept. LA-2084. 1955. Wagman, D. D. ; Evans, W. H. ; Halow, I. ; Parker, V. B. ; Bailey, S. M. ; Schumm, R. H. Nat. Bur. Stand. Tech. Note 270-3. 1968. 5. Cameron, A. E.; Withers, E. J. Amer. Chem. Sot. 1962, 84, 4175. 6. Burnett, J. L.; Cunningham, B. B. Lawrence Radiation Laboratory Rept. UCRL-11126. 1964. 7. Haschke, J. M.; Eick, H. A. J. Phys. Chem. 1969, 73, 374.
Enthalpy of formation monoxide? ELMER
J. HUBER,
of europium
Jr., and CHARLES
E. HOLLEY,
Jr.
University of California, Los Alamos Scientific Laboratory Los Alamos, New Mexico 87544, U.S.A. (Received I8 December 1968) The enthalpy of formation of europium monoxide (EuO~.~~) has been determined by means of oxygen bomb calorimetry and found to be A.HF(298.15 K, EuOl.& = - (143.3 4 0.5) kcal mol-l. A value of AHi(298.15 K, EuO) = - (135.0 * 1.3) kcal mol-’ was derived.
1. Introduction Little is known about the thermochemical properties of the lower oxides of the lanthanides. In fact, only EuO and Eu,O, are definitely known to exist. The compounds previously reported to be SmO and SmO,.,-,,, have been shown to be the nitride and hydride, respectively, and the existence of YbO must be considered doubtful.“) This paper reports the results obtained from the combustion of a sample of EuO in an oxygen bomb calorimeter. These results when combined with the enthalpy of formation of Eu,O,,(‘) yield the enthalpy of formation of EuO. The EuO was prepared by John Burnett (now of Oak Ridge National Laboratory) at the Lawrence Radiation Laboratory, University of California, Berkeley, in 1964 by the reaction of Eu with Eu,O,. Two separate batches of approximately equal quantity were made. The first analyzed as EuO~.~~~*~,~,,~, and the second as EuO~,,,~,-,~~,~~~. These determinations were made by Burnett by measuring the increase in mass upon oxidation. X-Ray analysis gave a = 5.1429 and 5.1428 A respectively for, these facecentered cubic materials. Twenty foreign metals were shown to be absent or present in amounts less than the limit of detection. The two samples were mixed prior to chemical analysis at Los Alamos and burning in the bomb. Chemical analyses gave H, 0.005 ; C, 0.0095; N, 0.020 mass per cent. Two samples were dissolved in 6 M hydrochloric acid solution, which had been distilled under vacuum, in the presence of platinum black. The volume of the gas evolved was measured and the percentage of hydrogen determined with a mass spectrograph. The platinum was used to catalyze the oxidation of Eu2+ by H+ and the production of the corresponding amount of hydrogen. An average value of EuO~.~~~*,,~,,~ was found for the composition of the monoxide which may indicate a slight oxidation during storage since the average of Burnett’s values is EuO,.,,,. The method involved the determination of the heat evolved from the combustion of a weighed sample of the europium monoxide at a known initial pressure of oxygen. t Work done under the auspices of the U.S. Atomic Energy Commission.
0 1 1 9
0.222 0.009 0.012 0.016
2.812 3.035 3.020 3.002
8 5 5 8
m(Eu0M.z (unburned)
m@uO)lg (burned) 31.1 11.2 17.2 17.2
TABLE
6.16 5.05 6.81 5.82
~OWmg wire)
(fuse
1. Energy of combustion
2 2 2 2
391.4 390.8 390.8 390.8
C/Cal K-1
of europium
1 0 0 1
AL&al
0.398 0.429 0.429 0.424
6.4 5.6 5.7 5.8 average : standard deviation of mean:
AT/K
monoxide
-323.3 -326.2 -324.3 -324.3 -324.5 0.6
AeJcal g-l
ENTHALPY
OF FORMATION
OF EUROPIUM
MONOXIDE
303
The method and equipment have been described. (3) Because of the limited amount of material available, only four runs were made. For the first run the combustion was carried out on discs of Eu,O, resting on a platinum stand. For the succeeding runs a platinum dish resting on a Eu,O, disk contained the coarse powder. The mass of platinum was 109.5 g in the first case and 122.1 g in the other three. The runs were made at 25 atm oxygen pressure. The energy equivalent C of the calorimeter was (2385.7kO.7) cal K-’ as determined with standard benzoic acid (NBS sample 39i). The calorie is the defined thermochemical calorie equal to 4.184 J. Temperature measurements were made with a platinum resistance thermometer and a Mueller bridge. Because of the possible reaction of the atmosphere with the oxide, the weighing of the material and loading of the bomb were carried out in a dry, inert-atmosphere box. When a sample of the material was subjected to 25 atm pressure of oxygen for one hour, a small (0.03 per cent) increase in mass was noted. A 0.01 in diameter magnesium fuse wire was used to ignite the samples. Its energy of combustion was taken as 5900 cal g-‘. The electrical energy required to ignite the fuse wire was measured with a current integrator. A microscopic examination of a combustion product showed no cubic phase of Eu,O, present. X-Ray analysis revealed only the monoclinic (B) form. Each combustion product was analyzed for completeness of combustion by dissolving in 6 M hydrochloric acid solution, as has been described above. The completeness of combustion thus determined was low for the first run (93 per cent) but high (> 99 per cent) for the next three runs.
2. Results Listed in table 1 are the results of the four runs. Shown in column (1) is the amount of sample burned after subtraction of the unburned material as listed in column (2). A,?& is the electrical energy used to ignite the fuse wire. The average, - 324.5 cal g-r, has a standard deviation of the mean of 0.6 cal g-‘. Corrections were applied for the impurities present. It was assumed that EuH,, EuC, and EuN were the contaminants which contributed to the energy of combustion in accordance with their enthalpies of formation and those of their combustion products. These enthalpies were taken to be A.H,“(EuH,) = -45 (estimated), AH,“(EuC) = -25 (estimated), AH,“(EuN) = -70 (estimated), AHF(C02) = -94,(4’ AHfO(H20,g) = -58,c4’ and AHf”(Eu,O,) = -393.9 kcal mol -’ .(‘) It was assumed that the nitride burned to nitrogen. The impurity correction reduced the magnitude of the combustion value by 2.06 per cent to - (317.8 f 1.8) cal g- ‘. The uncertainty given for the final value is twice the standard deviation of the mean combined with the uncertainty in the determination of the energy equivalent of the calorimeter and an estimated uncertainty for the impurity correction. Correction to unit fugacity of oxygen and to a constant pressure process leads to AH” = -(107.3 f0.6) kcal mol-’ for the reaction 2 Eu01,02(~)+0.48
O,(l atm) = Eu,O,(mono.)
The 1961 atomic weights were used. (‘) The A(PV) term amounted to 0.29 kcal mol-’ and the correction for non-ideality of oxygen to 0.04 kcal mol-‘.
304
The combination
E. J. HUBER,
JR. AND
C. E. HOLLEY,
JR.
3. Discussion of this reaction with 2 Eu(s)+ j- 02(1 atm) = Eu,O,(mono.); AH: = -(393.9+0.9) kcal mo1-1,(2)
yields AH~(Eu01.c2) = -(143.3 +0.5) kcal mol-‘. If the assumption is made that the EuO,,,, is a mixture of EuO and Eu,O,(mono.) then the material may be considered to be Eu0.0.021 Eu,O,. AH,“(EuO) may be calculated by taking AH,“(EuO) = { - 143.3 +0.5+(0.021+0.003)(393.9 +0.9)} kcal mol-‘, = -(135.0+1.3) kcal mol-‘, where the uncertainty now includes the uncertainty in the determination of the formula. Burnett and Cunningham (@ have reported AH,“(EuO) = - 145.2 kcal mol- ’ from enthalpies of solution of the metal and of EuO,.,, in HCl solutions. Haschke and Eick”’ have found AH,“(EuO) = -(145.2f4.1) kcal mole1 from an effusion method. The reason for the discrepancy is not apparent.
The authors thank John L. Burnett for preparing the samples of europium monoxide and supplying X-ray and spectroscopic analyses. They appreciate the work of Finley Ellinger, X-ray analysis of the combustion product, and of Carolyn MacDougall and Bert Baca, chemical analysis. REFERENCES 1. 2. 3. 4.
Felmlee, T. L. Thesis, Arizona State University. 1967. University Microfilm Order No. 67-7359. Huber, E. J., Jr.; Fitzgibbon, G. C.; Holley, C. E., Jr. J. Whys. Chem. 1964, 68, 2720. Holley, C. E., Jr.; Huber, E. J., Jr. Los Alamos Scientific Laboratory Rept. LA-2084. 1955. Wagman, D. D. ; Evans, W. H. ; Halow, I. ; Parker, V. B. ; Bailey, S. M. ; Schumm, R. H. Nat. Bur. Stand. Tech. Note 270-3. 1968. 5. Cameron, A. E.; Withers, E. J. Amer. Chem. Sot. 1962, 84, 4175. 6. Burnett, J. L.; Cunningham, B. B. Lawrence Radiation Laboratory Rept. UCRL-11126. 1964. 7. Haschke, J. M.; Eick, H. A. J. Phys. Chem. 1969, 73, 374.