Tracer diffusion coefficient of oxide ions in LaCoO3 single crystal

The tracer diffusion coefficient, $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$, of oxide ions in LaCoO₃ single crystal was determined over the temperature range of 700–1000°C by a gas-solid isotopic exchange technique using ¹⁸O tracer. For the determination, two methods, the gas phase analysis and the depth profile measurement, were employed. Under an oxygen pressure of 34 Torr, the temperature dependence of $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ in LaCoO₃ was expressed by

$\text{D1}{}_{\mathrm{<mtext>O</mtext>}}\text{(}\text{cm}{}^2\text{·}\text{sec}{}^{\mathrm{?1}}\text{) = 3.63 × 10}{}^4\text{exp}\text{?}\text{(74 ± 5)}\text{kcal}\text{·}\text{mole}{}^{\mathrm{?1}}\text{RT}$

$\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ at 950°C was found to be proportional to P^?0.35_O2. The diffusion of oxide ions occurs through a vacancy mechanism. The activation energy for the migration of oxide ion vacancies was estimated as 18 kcal · mole^?1.     

Electrical conductivity in strontium titanate

The electrical conductivity of polycrystalline SrTiO₃ was determined for the oxygen partial pressure range of 10° to 10^?22 atm and temperature range of 800 to 1050°C. The data were found to be proportional to the $\text{?1}\text{6}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range 10^?15–10^?22 atm, proportional to for the oxygen pressure range 10^?8–10^?15 atm, and proportional to for the oxygen pressure range 10⁰–10^?3 atm. These data are consistent with the presence of very small amounts of acceptor impurities in SrTiO₃.     

Laser-molecular beam measurement of hyperfine structure in the I2 spectrum

Very high resolution measurements of hyperfine structure on the P(13) and R(15), 43?0, $\text{3}{}_{\mathrm{gp}}{}_0{}^{\mathrm{+}}{}_{\mathrm{u}}\text{←}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ transitions in iodine 127 were made using laser molecular beam spectroscopy. The observed linewidth was 300 kHz (fwhm) giving a resolution of 5 × 10^?10 The observed spectrum was fitted to obtain a quadrupole coupling strength difference of ΔeQq = 1906 ± 2 MHz and a spin rotation interaction strength difference of ΔC_I = 181 ± 7 kHz between the upper and lower levels of the P(13) transition. For the R (15) transition ΔeQq = 1905 ± 2 MHz and ΔC_I = 167 ± 5 kHz.     

Hydrodynamic properties and equilibrium rigidity of polyamidobenzimidazole molecules in dimethylacetamide and sulphuric acid

Translational diffusion, velocity sedimentation and viscometry of polyamidobenzimidazole (PABI) solutions in the range of M = (1–61) · 10³ have been investigated in N,N-dimethylacetamide (DMA) and 98% H₂SO₄. The dependences of D₀, S₀ and [η] on M were obtained. Tsvetkov-Klenin's hydrodynamic invariant was found to be $\text{A}{}_0\text{= 3.55 · 10}{}^{\mathrm{?10}}\text{erg deg}{}^{\mathrm{?1}}\text{mol}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$. The equilibrium rigidity of PABI molecules was characterized by the length of the Kuhn segment $\text{A = 250 ± 100}\text{A}\text{?}$. The chain diameter was $\text{7 ± 4}\text{A}\text{?}$. The values of A in 98% H₂SO₄ and in an aprotic solvent, DMA, were virtually identical, implying that the rigid-chain conformation of PABI molecules in 98% H₂SO₄ is due to their geometrical structure rather than to the protonization of amide bonds. The significance of the latter evidently increases in PABI solutions in 100% H₂SO₄ in which A is 1.5 times as high. The decrease in rigidity of PABI as compared to that of poly-p-phenylene terephthalamide ($\text{A = 400 ± 100}\text{A}\text{?}$) is in reasonable agreement with the presence of imidazole rings in PABI molecules. The presence of these rings results in kinks in the PABI chain with angles of about 30° and hence, in the depature from parallelism of rotating bonds.     

Electrical conductivity in calcium titanate

The electrical conductivity of polycrystalline CaTiO₃ was measured over the temperature range 800–1100°C while in thermodynamic equilibrium with oxygen partial pressures from 10^?22 to 10⁰ atm. The data were found to be proportional to the $\text{?}\text{1}\text{6}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range 10^?16 – 10^?22 atm, proportional to for the oxygen pressure range 10^?8 – 10^?15 atm, and proportional to for the oxygen pressure range greater than 10^?4 atm. The region of linearity where the electrical conductivity varies as $\text{?}\text{1}\text{4}\text{th}$ power of P_O2 increased as the temperature was decreased. The observed data are consistent with the presence of small amounts of acceptor impurities in CaTiO₃. The band-gap energy (extrapolated to zero temperature) was estimated to be 3.46 eV.     

Electrical conductivity in strontium titanate with nonideal cationic ratio

The electrical conductivity of polycrystalline strontium titanate with ($\text{Sr}\text{Ti}\text{= 0.996, 0.99,}\text{and}\text{0.98}$ was determined for the oxygen partial pressure range of 10⁰ to 10^?22 atm and the temperature range of 850–1050°C. These data were found to be similar to that obtained for the sample with ideal cationic ratio. The observed data were proportional to the $\text{?}\text{1}\text{6}$ power of oxygen partial pressure for P_O2 < 10^?15atm, proportional to for the pressure range 10^?8–10^?15 atm, and proportional to for P_O2 > 10^?4atm. The deviation from the ideal Sr-to-Ti ratio was found to be accommodated by neutral vacancy pairs, (V″_Sr V″₀. The results indicate that the single-phase field of strontium titanate extends beyond 50.505 mole% TiO₂ at elevated temperatures.     

Hydrodynamic properties and statistical coil dimensions of poly(o-chlorostyrene)

The theta temperature for the system poly(o-chlorostyrene)-methyl ethyl ketone has been determined as 24·5°. The samples used in the determination were prepared by radical polymerization. The dependence of intrinsic viscosity on molecular weight has been measured in methyl ethyl ketone at 24·5° and found to be $\text{η}{}_{\mathrm{\theta }}\text{= 4·68 × 10}{}^{\mathrm{?4}}\text{M}{}_{\mathrm{<mtext>w</mtext>}}{}^{\mathrm{<mtext>M1</mtext><mtext>2</mtext>}}$. The ratio 〈s₌²〉/M was found, by light scattering, to be 5·60 × 10^?18 cm². Analysis of the solution properties indicates that the Kurata-Yamakawa theory is valid in the vicinity of the Flory temperature (UCST).     

Polymerisation radiochimique de l'acetaldehyde en phase solide

The radiation induced solid-state polymerization and post-polymerization of crystalline acetaldehyde were studied in a diathermic calorimeter by measuring the heat evolution during polymerization. The heat of melting of crystalline acetaldehyde was found to be 1,4 ± 0,07 kcal mol^?1 and the heat of polymerization 2,5 ± 0,5 kcal mol^?1 at 80–150°K. Under isothermal conditions the rate of the solid state polymerization of acetaldehyde increased with irradiation time up to a maximum and thereafter it decreased. This phenomenon is connected with an increase of the concentration of active centres during irradiation. The propagation rate constant is $\text{k}{}_{\mathrm{p}}\text{? 5 × 10}{}^{\mathrm{?4}}\text{exp(?11,000/RT) cm}{}^3\text{sec}{}^{\mathrm{?1}}$ at 130–140°K and the average time of addition of one monomer unit is 10^?1–10^?2 sec.     

Electrical conductivity and defect structure of Nd2O3+x

The electrical conductivity and departure from the stoichiometry of Nd₂O₃ have been measured over the temperature range of 900° to 1100°C and oxygen partial pressure of 1 to 10^?16 atm. The hole conductivity of Nd₂O₃ is found to be proportional to , where n are 4.6, 4.9, and 5.1 at 900°, 1000°, and 1100°C, respectively. From the oxygen partial pressure dependence of the hole conductivity, it is shown that the predominant point defects in nonstoichiometric NdO_1·+x are fully ionized and partially doubly ionized metal vacancies. From the thermogravimetric measurements, the departure from stoichiometry, x in NdO_1·5+x, is 2.0 × 10^?3 at 1000°C and 1 atm. By combining the electrical conductivity and weight change data, it is shown that the hole mobility is 6.3 × 10^?4 (cm²/V·sec) at 1000°C and 1 atm.     

Electronic conductivity in nonstoichiometric cerium dioxide

The electrical conductivity of sintered specimens of nonstoichiometric CeO_2?x was measured as a function of temperature (750–1500°C) and oxygen pressure (1–10^?22 atm). The isothermal compositional dependence of the electrical conductivity of CeO_2?x was determined by combining recently obtained thermodynamic data, x = x(P_O2, T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expression

$\text{σ=410[x]e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{ohm cm}\text{)}{}^{\mathrm{?1}}$

over the temperature range 750–1500°C and from x = 0.001 to x = 0.1.This expression was rationalized in terms of the following simple relations for (a) the electron carrier concentration

$\text{n}{}_{\mathrm{ce}}\text{′}{}_{\mathrm{ce}}\text{=}\text{8x}\text{a}{}_0{}^3$

where n_Ce′Ce is the number of Ce′_Ce per cm³ and a₀ is the lattice parameter and (b) the electron mobility

$\text{μ=5.2(10}{}^{\mathrm{?2}}\text{)e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{cm}{}^2\text{/}\text{V sec}\text{)}$

.     

Chainlength effects on interactions of polyvinylpyrrolidone with low and high molecular compounds

Very narrow fractions of polyvinylpyrrolidone (PVP) for a range of low molecular weight from 20·10³ to $\text{\&{;10}{}^3$ were prepared by gel filtration using sephadex gel. Interactions between fractions of different M_n and small molecules (iodine and 1-anilinonaphthaline-8-sulphonate) and polymers (polymethacrylic and polyacrylic acids) were studied in aqueous solution. The ability of PVP to form complexes with low molecular weight compounds depends on chainlength. The greatest loss of the ability was observed for PVP with M_n on passing from 5·10³ to $\text{\&{;10}{}^3$. The chainlength effects for PVP are accounted for an unlike dehydration and unlike “local” link concentration near links for these macromolecules in water. For PAA and PMAA. the threshold values of M?_n, below which there is the beginning of weakening of complexation for PVP, are 6·10³ and 2.5·10³ respectively. The difference of the complex formation for these polyacids appears to be related to hydrophobic interactions between the χ-methyl groups of PMAA and nonpolar regions of PVP.     

Struktur und Bindung in Übergangsmetall-Fluoriden MIIMeIVF6: Neutronenbeugungs-Strukturuntersuchungen an CaSnF6, FeZrF6, und CrZrF6

Compounds M^IIMe^IVF₆ requently undergo phase transitions from the cubic ordered ReO₃ to the trigonal LiSbF₆ structure when lowering the temperature. In case of a strongly Jahn-Teller unstable cation in the M^II position additional phases may occur. Results of powder neutron-diffraction studies on CaSnF₆, FeZrF₆, and CrZrF₆ at different temperatures are reported. The high-temperature phases have the space group Fm3m; the F^? ligands are either statistically displaced from the M^IIMe^IV directions or undergo a strong thermal motion perpendicular to these directions ($\text{?M}{}^{\mathrm{<mtext>II</mtext>}}\text{}\text{FMe}{}^{\mathrm{IV}}$: 165–180°). The thermal ellipsoids of the CrF bonds are strongly indicative of a dynamical Jahn-Teller effect in addition. In the low-temperature phases of CaSnF₆ and FeZrF₆ (space group $\text{R}\text{3}$) the $\text{?M}{}^{\mathrm{<mtext>II</mtext>}}\text{}\text{FMe}{}^{\mathrm{IV}}$ is more distinctly bent (?155–160°). CrZrF₆ undergoes two reversible phase transitions, which are determined to occur at 415 ± 5 K (cubic → tetragonal, dynamic to static Jahn-Teller distortion of CrF₆ octahedra and 150 ± 10 K (tetragonal → (pseudo)monoclinic).     

Nonstoichiometry and defect structure of the perovskite-type oxides La1−xSrxFeO3−°

In order to elucidate the defect structure of the perovskite-type oxide solid solution La_1?xSr_xFeO_3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, P_O2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of P_O2 ≥ 0.13 atm, δ in La_1?xSr_xFeO_3?δ was found to be close to 0. With decreasing log P_O2, δ increased and asymptotically reached $\text{x}\text{2}$. The value corresponding to $\text{δ =}\text{x}\text{2}$ was about ?10 at 1000°C. With further decrease in log P_O2, δ slightly increased. For LaFeO_3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log P_O2 is interpreted on the basis of the defect equilibrium among Sr′_La (or V?_La for the case of LaFeO_3?δ), V^··_O, Fe′_Fe, and Fe^·_Fe. Calculations were made for the equilibrium constants K_ox of the reaction

$\text{1}\text{2}\text{O}{}_2\text{(g) + V}{}^{\mathrm{··}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= O}{}^{\mathrm{x}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe}}$

and K_i for the reaction

$\text{2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= Fe}{}^{\mathrm{\prime }}{}_{\mathrm{Fe}}\text{+ Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe·}}$

Using these constants, the defect concentrations were calculated as functions of P_O2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.     

The reorientation of Cd2+-vacancy and Pb2+-vacancy complexes in KCl

The relaxation of Pb²⁺-vacancy and Cd²⁺-vacancy dipoles in purified KCl crystals was studied using a double crystal dc polarization method which self-corrects relaxation effects due to spurious causes. In the radius range from Cd²⁺ to Ba²⁺ these results and most others support Dreyfus' model. The reciprocal relaxation times for each impurity are given by

$\text{τ}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>Cd</mtext>}}\text{=2.06x10}{}^{12}\text{exp(?s0.64±0.01}\text{eV}\text{)}\text{kT}$

;

$\text{τ}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>Pb</mtext>}}\text{=1.19x10}{}^{13}\text{exp(?0.69±0.01}\text{eV}\text{)}\text{kT}$

.It is also shown that the presence of H₂O or its products greatly perturb the relaxation times observed.     

The reaction of nitric oxide with vibrationally excited ozone

The reaction between nitric oxide and vibrationally excited ozone was studied in a fast flow reactor by monitoring the visible emission from electronically excited NO₂¹. The antisymmetric mode (ν₃) of O₃ was excited with a Q-switched 9.6 μm CO₂ laser, and a laser-induced signal was detected, with a rise rate constant of (4.0 ± 0.5) × 10¹¹ cm³/mole sec and a decay rate constant of (1.1 ± 0.1) × 10¹¹ cm³/mole sec for an NO-rich mixture. The latter was unaffected by addition of large amounts of He or Ar, indicating that the signal was not a thermal effect. Most of the measurements were made at 350°K; however, the He and Ar dilution results suggest that the enhanced reaction rate is not very sensitive to temperature. In order to explain the observed rise times, it was necessary to postulate an intermediate step prior to the chemical reaction. A model which is consistent with our data has energy transferred from ν₃ to ν₂ (the bending mode) at a rate of (2.9 ± 0.5) × 10¹¹ cm³/mole sec for NO and a rate of (1.1 ± 0.2) × 10¹¹ cm³/mole sec for He. According to this model, the rate constant for the reaction of NO with O₃ (ν₂= 1) producing vibrationally excited ground state NO₂²,

$\text{NO + O}{}_3{}^2\text{(010)}\text{3}\text{NO}{}_2{}^2\text{+ O}{}_2$

is (1.5 ± 0.2) × 10¹¹ cm³/mole sec, and the relative rate for the reaction of O₃ (ν₂ = 1) and O₃(ν₂ = 0) with NO was estimated to be $\text{k}{}_3\text{(1)}\text{k}{}_3\text{(0)}\text{≈ 22}$.     

Standard enthalpy of solution and formation of cesium chromate. Derived thermodynamic properties of the aqueous chromate,bichromate, and dichromate ions,alkali metal and alkaline earth chromates,and lead chromate

Calorimetric measurements of the enthalpy of solution of cesium chromate gave ΔH_soln = (7622 ± 24) cal_th mol^?1 for a dilution of Cs₂CrO₄·21128H₂O. This result, along with the enthalpy of dilution gave the standard enthalpy of solution, ΔH_soln^o = (7512 ± 31) cal_th mol^?1, whence the standard enthalpy of formation, ΔH_f⁰(Cs₂CrO₄, c, 298.15 K), was calculated to be ?(341.78 ± 0.46) kcal_th mol^?1. Recomputed thermodynamic data for the formation of the other alkali metal chromates have been tabulated. From their solubilities and enthalpies of solution, the standard entropies, S⁰(298 K), of BaCrO₄ and PbCrO₄ were estimated to be (38.9 ± 0.9) and (43.7 ± 1.2) cal_th K^?1 mol^?1, respectively. There is evidence that ΔH_f⁰(SrCrO₄, c, 298.15 K) may be in error. Thermochemical, solubility, and equilibrium data, have been combined to update the thermodynamic properties of the aqueous chromate (CrO₄^2?), bichromate (HCrO₄^?), and dichromate (Cr₂O₇^2?) ions. The new values at 298.15 K are as follows:

     

18.

Mutual solubility of n-butanol + water under high pressures     

Yasuhiro Aoki  Takashi Moriyoshi 《The Journal of chemical thermodynamics》1978,10(12):1173-1179

The mutual solubilities of {xCH₃CH₂CH₂CH₂OH+(1-x)H₂O} have been determined over the temperature range 302.95 to 397.75 K at pressures up to 2450 atm. An increase in temperature and pressure results in a contraction of the immiscibility region. The results obtained for the critical solution properties are: T_o(U.C.S.T.) = 397.85 K and x_o = 0.110 at 1 atm; $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(12.0±0.5)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at p < 400 atm and $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(7.0±0.7)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at 800 atm < p < 2500 atm; $\text{(}\text{dx}{}_{\mathrm{o}}\text{d}\text{T}\text{) = ?(4.0±0.5)×10}{}^{\mathrm{?4}}\text{K}{}^{\mathrm{?1}}$.     

19.

Thermochemical properties of benzoic acid derivatives XI. Vapour pressures and enthalpies of sublimation and formation of the six dimethylbenzoic acids     

M. Colomina  P. Jimenez  M.V. Roux  C. Turrion 《The Journal of chemical thermodynamics》1984,16(12):1121-1127

The energies of combustion of 3,4- and 3,5-dimethylbenzoic acids have been revised by combustion calorimetry. Vapour pressures of very pure samples of the six dimethylbenzoic acids have been determined over a range of temperatures near 298 K by the Knudsen-effusion technique. From the experimental results and our previously published thermochemical quantities the following results for the six C₆H₃(CH₃)₂CO₂H isomers at 298.15 K have been derived.

	$\text{S}{}^0\text{/}\text{cal}{}_{\mathrm{th}}\text{K}{}^{\mathrm{?1}}\text{mol}{}^{\mathrm{?1}}$	$\text{ΔH}{}_{\mathrm{f}}{}^0\text{/kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?1}}$	$\text{ΔG}{}_{\mathrm{f}}{}^0\text{/kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?1}}$
CrO42?(aq)	(13.8 ± 0.5)	?(210.93 ± 0.45)	?(174.8 ± 0.5)
HCrO4?(aq)	(46.6 ± 1.8)	?(210.0 ± 0.7)	?(183.7 ± 0.5)
Cr2O72?(aq)	(67.4 ± 3.9)	?(356.5 ± 1.5)	?(312.8 ± 1.0)

     

20.

Standard enthalpies of formation of uranium compounds I. β-UO₃ and γ-UO₃     

E.H.P. Cordfunke  W. Ouweltjes  G. Prins 《The Journal of chemical thermodynamics》1975,7(12):1137-1142

The standard enthalpy of formation of γ-UO₃ has been critically assessed; the value ?(292.5 ± 0.2) kcal_th mol^?1 is suggested.The enthalpies of solution of β-UO₃ and γ-UO₃ in 3 M H₂SO₄ have been measured and used to derive:

$\text{ΔH}{}_{\mathrm{f}}{}^{\mathrm{°}}\text{(β?}\text{UO}{}_3\text{, 298.15}\text{K}\text{) = ?(291.6 ± 0.2)}\text{kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?}}$

     

Isomer		$\text{Δ}{}_{\mathrm{<mtext>f</mtext>}}\text{H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(cr)}$	$\text{Δ}{}_{\mathrm{<mtext>sub</mtext>}}\text{H}{}_{\mathrm{m}}{}^{\mathrm{o}}$	$\text{Δ}{}_{\mathrm{<mtext>f</mtext>}}\text{H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(g)}$
	kJ·mol?1	kJ·mol?1	kJ·mol?1
2,6-	?440.7 ± 1.7	99.1 ± 0.2	?341.6 ± 1.7
2,3-	?450.4 ± 1.7	104.6 ± 0.4	?345.8 ± 1.7
2,5-	?456.1 ± 1.6	105.0 ± 0.6	?351.1 ± 1.7
2,4-	?458.5 ± 1.7	103.5 ± 0.3	?355.0 ± 1.7
3,4-	?468.8 ± 1.9	106.4 ± 0.3	?362.4 ± 1.9
3,5-	?466.8 ± 1.7	102.3 ± 0.3	?364.5 ± 1.7

Mutual solubility of n-butanol + water under high pressures

The mutual solubilities of {xCH₃CH₂CH₂CH₂OH+(1-x)H₂O} have been determined over the temperature range 302.95 to 397.75 K at pressures up to 2450 atm. An increase in temperature and pressure results in a contraction of the immiscibility region. The results obtained for the critical solution properties are: T_o(U.C.S.T.) = 397.85 K and x_o = 0.110 at 1 atm; $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(12.0±0.5)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at p < 400 atm and $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(7.0±0.7)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at 800 atm < p < 2500 atm; $\text{(}\text{dx}{}_{\mathrm{o}}\text{d}\text{T}\text{) = ?(4.0±0.5)×10}{}^{\mathrm{?4}}\text{K}{}^{\mathrm{?1}}$.     

Thermochemical properties of benzoic acid derivatives XI. Vapour pressures and enthalpies of sublimation and formation of the six dimethylbenzoic acids

The energies of combustion of 3,4- and 3,5-dimethylbenzoic acids have been revised by combustion calorimetry. Vapour pressures of very pure samples of the six dimethylbenzoic acids have been determined over a range of temperatures near 298 K by the Knudsen-effusion technique. From the experimental results and our previously published thermochemical quantities the following results for the six C₆H₃(CH₃)₂CO₂H isomers at 298.15 K have been derived.

Standard enthalpies of formation of uranium compounds I. β-UO3 and γ-UO3

The standard enthalpy of formation of γ-UO₃ has been critically assessed; the value ?(292.5 ± 0.2) kcal_th mol^?1 is suggested.The enthalpies of solution of β-UO₃ and γ-UO₃ in 3 M H₂SO₄ have been measured and used to derive:

$\text{ΔH}{}_{\mathrm{f}}{}^{\mathrm{°}}\text{(β?}\text{UO}{}_3\text{, 298.15}\text{K}\text{) = ?(291.6 ± 0.2)}\text{kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?}}$