NOTES
2464
1800"; the latter requires a temperature between 2000 and 3000". This situation seems to be similar in some respects to graphite damaged by neutron irradiation in which complete recovery occurs when the annealing temperature approaches 2000°.7-9 ~~
~
~
(7) M .Burton and T. J. Neubert, J . A p p l . Phys., 27, 557 (1956). (8) A. Herpin, J . phys. radium, 24, 499 (1963). (9) E. A . Kellott and H. P. Rooksby. G.E C. Journal, 31, 28 (1964).
The Heat of Formation of Lanthanum Oxide' by George C. Fitzgibbon, Charles E. Holley, Jr., Uniaersity of California, Los Alamos Scientific Laboratory, Los Alamos, S r w Mexico
and Ingeniar Wadso Thermochemistry Laboratory, University of L u n d , L u n d , Sweden (Receired December 83, 2964)
Values of the heats of solution of lanthanum metal and lanthanum oxide are presented as determined in calorinieters previously d e s ~ r i b e d and, , ~ ~ ~in conjunction with the heat of formation of liquid water from its e l e ~ n e n t sare , ~ used to determine the heat of formation of Laz03.
Experimental The calorimeter used in Los Alamos is an isothermal solution calorimeter whose environmental temperature niay be kept constant a t any setting between 23 and 33" to within 0.001" in an 800-1. thermostatically controlled bath. The vacuum-j acketed, silver-bodied, platinum-lined calorimeter reaction vessel has a volume of -450 cc., a thermal leak modulus of O.O05/min., and a heat capacity of 420 cal. Within the reaction chaniber are a heater, a thermistor, a Pyrex rod to which is attached a platinum stirrer, and a glass sample bulb. The heater consists of a lrj.23-cni. length of 0.64-cni. 0.d. platinum tubing, the lower end gold soldered, the upper end sealed to glass tubing which extends through the calorimeter lid and carries the heater leads. The platinum tubing contains 23 o h m of bifilarly wound, helirally coiled, sill,-covered iiiangaiiin wire with leads to measure the voltage drop, located at the solution level. A Fenwall 2300-ohm tht~rniistorIS used as the sensing element to iiieasure temperature differences up to 1.6" to within 0.0001". h Brown recorder was modified to an automatic changing iiiultiscale self-balancing WheatThe Journal of Physical Chemistry
stone bridge, whose arm position is an indication of the resistance of the thermistor. The energy equivalent is determined by passing a current from a precision voltage-regulated supply through the calorimeter heater and a 0.1-ohm standard resistor in series and measuring the voltage drops using a Rubicon Type B potentiometer and a Rubicon reflecting galvanometer. The input time is read directly from an electronic decade counter whose time base is derived from a 100-kc. crystal-controlled oscillator, accurate and stable to O . O l ~ o . The lanthanum metal was obtained from the Anies Laboratory, hmes, Iowa, in the form of a small ingot, through the courtesy of Prof. F. H. Spedding. I t was prepared before each run by filing the surfaces to a shiny luster before cutting off several small pieces. The sample size was chosen to give a temperature rise The composition of the saiiiple, calculated of -1". from an analysis, is: La, 98.810; JIg, 0.003; Ca, 0.010; Fe, 0.050; L a x , 0.164; Laz03, 0.146; Lac2, 0.047; LaH2,0.768. The hydrated sesquioxide mas obtained from the Michigan Chemical Co. I t was treated by heating in an induction furnace, under vacuum, to 1200" in an alunduni crucible for about 1 hr. It was then transferred to a drybox for weighing and sealing in a sample bulb. The oxide sample used in Lund was further treated before use by heating in air at 1030" for about 30 min. in a platinum crucible. It was then stored under dry S p for about 1 hr. before being put into a calorimetric ampoule. The coniposition of the oxide sample, calculated from an analysis, is : La203, 99.882; SiOz, 0.002; BaO, 0.006; CaO, 0.040; Fe203, 0.070. The heats of solution of this lanthanum metal and oxide were determined in 1.00 HC1 saturated with hydrogen. The average duration of a run was 10 min. from the breaking of the sample bulb until equilibrium was reached in the after period. Weights are given in vacuo. The defined calorie (4.1840 absolute joules) is used in expressing the results. The atomic weight used for lanthanuni is 138.91. The sample sizes of metal and oxide were adjusted so ihat the final solution in both cases had approximately the same composition, i.e., ca. 0.0065 -11 in LaC13 and with enough excess of HC1 that its concentration changed only (1) Work done in part under the auspices of the U. S.Atomic Energy Commission. (2) G . C . Fitzgibbon, D. Pavone, E. J. Huber, Jr., and C . E. Holley, Jr.. Los Alamos Scientific Laboratory Report. LA-3031 (1964). (3) S.Sunner and I. Wadso, Acta Chem. Scand.. 13, 97 (1959). (4) "Selected Values of Chemical Thermodynamic Properties," National Bureau of Standards Circular 500, U. S. Government Printing Office, Washington, D. C . . 1952.
NOTES
2465
slightly. The results of the experiments on lanthanum metal are shown in Tables I and 11.
Table I: Heat of Solution of Lanthanum Metal-Los Alamos Results MWS of La, B.
Mass of solvent, g.
0.36589 0.36587 0.36640 0.36633 0.36665 0.36678
399.41 399.38 399.95 399.88 400.23 400.37
Energy equiv., cal./ Temp. rise, arbitrary arbitrary unit unit
17.003 17.046 17.009 17.056 17.001 17.030
26.122 26.060 26.150 26.076 26.159 26.120
composition of the solution was approximately the same as for the metal solutions. The results are shown in Tables I11 and IV.
Table 111: The Heat of Solution of Lanthanum Oxide-Los Alamos Results Energy from La, cal./g.
Dev., cal./g.
1204.2 1204.2 1204.2 1204.4 1203.2 1203.2
Av. 1203.9 Correction for HzO evap. 5.0 Heat of solution of La metal 1208.9 2 X std. dev. of the mean
0.3 0.3 0.3 0.5 0.7 0.7 0.5
Mass of LarOa, g.
Mass of solvent, g.
Energy equiv., cal./ arbitrary unit
0.43030 0.43000 0.43020 0.43080 0.42920 0.42955
400.50 400.22 400.40 400.97 399.48 399.80
16.752 16.789 16.749 16.721 16.690 16.720
2
0.4 -
x
Temp. rise, arbitrary unit
Energy from Laz03, cal./g.
Dev., cal./g.
8.940 8.914 8.929 8.975 8.941 8.951
348.08 348.04 347.65 348.38 347.71 348.44
0.03 0.01 0.40 0.33 0.34 0.39
Av. 348.05 std. dev. of the mean
0.25 0.26
~~
Table IV : Heat of Solution of Lanthanum Oxide-Lund Results"
Table I1 : Heat of Solution of Lanthanum Metal-Lund Results" Mass of La, g.
0.09326 0,09119 0.09759 0.09658 0.09400
Temp. rise, arbitrary unit
12.504 12,212 13,064 12,921 12.600
Energy from La, oal./g.
1206.4 1205.0 1204.5 1203.8 1206.1
Av. 1205.2 Correction for HzO evap. 3.8 Heat of solution of La metal 1209.0 2 x ntd. dev. of the mean
Dev., cal./g.
1.2 0.2 0.7 1.4 0.9 0.9 1.0
Mass of LaPOa, g.
Temp. rise, arbitrary unit
Energy from LazOa, cal./g.
Dev., cal./g.
0,10031 0.10086 0.10054 0.10009 0.10037
3.947 3.975 3.961 3.938 3.950
347.44 348.00 347.88 347.41 347.50
0.21 0.35 0.23 0.24 0.15
Av. 347.65 2 X std. dev. of the mean
0.24 0 26
__
'Mass of solvent = 101.50 g.; energy equivalent (mean value) = 8.830 cal./arbitrary unit.
a Mass of solvent = 101.50 g.; energy equivalent (mean value) = cal./arbitrary unit.
The uncertainty in the heat for the evaporation of the HzO by the escaping Hz is taken as 10% or 0.07 kcal./mole. Heats of alloy formation are ignored. The value of the correction for the impurities, with its uncertainty, is -0.69 f 0.30 kcal./mole. The corrected value for the heat of solution of La met,al in 1 M HC1 a t 298" is thus -168.62 f 0.32 kcal./mole from the Los Alanios results and -168.63 f 0.32 kcal./mole from the Lurid results. These values are both in good agreement with the value -168.77 f 0.20 reported by Spedding and Flynn . The heats of solution of the lanthanum oxide were determined in HC1 saturated with H 2with the amounts of oxide and acid adjusted so that the final
The correction for impurities was made on the assumption that the oxide had the composition given earlier and that the Si02 was inert. The possibility of the formation of mixed oxides was ignored. The correction for impurities amounts to 0.02 kcal./niole giving a corrected value for the heat of solution of hexagonal lanthanum oxide in 1 HCl of - 113.38 f 0.09 kcal./niole from the Los Alamos results and -113.25 f 0.09 kcal./mole from the Lurid results. Both values are in good agreement with the value of - 113.38 f 0.37 kcal./niole reported by llontgomery6 for somewhat different concentrations. (6) F. H. Spedding and J. P. Flynn, J. Am. Chem.
SOC.,
76, 1476
(1964).
(6) R . L. Montgomery, U, S. Department of the Interior, Bureau of Mines, Report of Investigations No. 6446, Pittsburgh, Pa., 1969.
Volume 69, iyumber 7
J u l y 1966
NOTES
2466
Comparison of Results The results from the two laboratories are summarized in Table V. In addition, results are also shown for the heat of solution of Tris, which has been proposed for use as a comparison material for solution calorimeters'' It appears that the g;ve results which agree with each other, within the precision of the measurements, on these three rather diverse materials. Table V : Comparison of Heat of Solution Results Obtained a t Los Alamos and a t Lund of solution, cal.,g
Lametal La203 Tris
(uncor,iF
Difference
(L,A,-
Los hlamos
Lund
Lurid), %
1203.9 f 0 . 4 348.05 f 0.26 7116 f8
1205.2 f 1 . 0 347.65 f 0.26 7107 f4
-0.11 +0.11 + O . 13
Table VI: The Heat of Formation of Laz03 at 298°K. Reaction
+ + + +
-
1. 2La(s) GHCl(aq) 2LaC13(aqj 3Hz(g) 2. Laz03(s) 6HCl(aq) 2LaC13(aq) 3Hz0(1) 1.50z(g) 3. 3Hdg) 3H20(11 1.502(g) 4. 2La(sj LazOd s j AH = AH1
+ +
7 -
AH,kcal./mol--Loa Alamos
Lund
337.24 f 0.64 337.26 f 0 , 6 4 113.38 f 0.09 113.25 f 0.09
-
204.96 f 0.03 204.96 f 0.03 428.82 f 0.64 428.97 f 0.64
+ AH3 - AHz
Viscosity of Glass-Forming Solvent
Mixtures at Low Temperatures
by Hina Greenspan and Ernst Fischer Photochemical Laboratory, The Weizmann Institute of Science, Rehovoth, Israel (Received December $3, 1964)
The viscosity of solvent mixtures has a pronounced effect on bimolecular reactions, such as photosensitized reactions' and second-order triplet decay.2 In monomolecular reactions, such as photoinduced molecular rearrangements, the role of high viscosities is less pronounced but still marked. Thus, it was observed that the internal rearrangement of merocyanines, after their formation by irradiation of the corresponding spiropyrans, is slowed down sharply in hydrocarbon g l a s ~ e s ,apparently ~ by the combined effect of low temperature and high viscosity. Similarly, the thermal tautomerization of 1-phenylazo-2-naphthol following photoisomerization was found4 to be slowed down by cooling their solutions in hydrocarbon mixtures to - 185' or in plastic films to about - 100". The macroscopic viscosity is clearly not identical with the "microscopic" one a t the molecular level. However, one may expect a rough parallelism between the two, a t least in chemically similar media. It was therefore interesting to get an idea of the viscosities of these glasses a t temperatures down to that of liquid nitrogen-if not directly, then a t least by extrapolation from temperatures a t which the viscosity is already high, though still measurable.
Experimental The Heat of Formation of La203. The calculation of the heat of formation of lanthanum oxide is shown in Table VI. These values agree with each other within the estimated uncertainties and they both agree with the conibustiori value, -428.57 f 0.19 kcal./mole, obtained by Huber and Holley.8 The weighted average of these three sets of measurements is -428.6 f 0.2 kcal./inole. The heat of formation of hexagonal LazO3can now be regarded as having been determined to within rather narrow limits (about O.lOj,) by two independent methods.
Since the ordinary viscosimetric methods cannot easily be applied a t very high viscosities, a penetrometric method was employed in which one measured the penetration rate of a 3-mm. glass rod, carrying a weight of up to 400 g., into the solvent mixtures a t various temperatures. This is described schematically in Figure 1, where the weight is an iron core, released a t a suitable moment by switching off an external electromagnet. In the apparatus described, the solvents are distilled in a high vacuum system5 into the
A4cknowledg,?zent, Grateful acknowledgment is extended to 'Ir' Pavone for his preparation Of the oxide samples.
(1) S. Malkin and E. Fischer, J . Phys. Chem., 68, 1153 (1964). (2) (a) G. Porter and F. Wilkinson, Proc. Roy. Soc. (London), AZ64, 1 (1961); (b) G. Oster and Y, Nishijima, Fortschr, Hockpolym. Forsch., 3 , 313 (1964). (3) (a) R. Heiligman-Rim, Y. EIirshberg, and E. Fischer. J . Phys. Chem., 6 6 , 2470 (1962); (b) T.Bercovici and E. Fischer, to be published. and E. Fischer*to be published. (4) G. (5) Y.Hirshberg and E. Fischer, Rev. Sci. Instr., 30, 197 (1959)
(7) K.J. Irving and I. Wadso, Acta Chem. Scand.. 18, 196 (1964). ( 8 ) E. J. Huber. J r . , and C. E. Holley. Jr., J . A m . Chem. SOC.,7 5 , 3594 (1953).
The Journal of Physical Chemistry
