Third-law heats

Judged most acceptable. The third-law heat of reaction derived from their data is adopted and combined with the heat of formation... 

The recent study by Bradbury and Ohse (28) extends measurements to 2219 K and 9.5 x 10 atm, connecting smoothly to earlier, lower-temperature data. The second-law and third-law heats of vaporization of 82.25 and 81.66 kcal/mol, respectively, are in quite good agreement with the summary assessment in Ref. 19. 

Second-law and third-law heats were in close agreement, to give Ah298 = 46900 + 300 cal/mol as the heat of vaporization. The... 

Table V-8 Third law heat of sublimation values for gaseous zirconium including the p-T equation and the temperature range over which the measurements were conducted.

Ion intensities were measured for daughter ions of each of the gases in Reaction (V.28) from which an equilibrium constant for the reaction, at each temperature investigated, was derived. From the equilibrium constants, a third law heat of reaction was calculated ... 

Ion intensities were measured for daughter ions of each of the gases in the reactions, from which the equilibrium constants, at each temperature investigated, were derived. From the equilibrium constants, third law heat of reactions were calculated. The third law heat of reaction derived for Reaction (V.43) was of low accuracy [70POT] and, as such, was not used in the derivation of the heat of formation of ZrCl3(g). Data from Reactions (V.44) and (V.45) were then combined with the selected... 

The third law heat of reaction obtained for Reactions (V.47) and (V.48) by [70POT] were (37 25) and -(51.5 7.9) kJ-mol", respectively. These values were then combined with the selected enthalpies of formation for ZrCl3(g) and ZrCl2(g) (see above), B(g) (Chapter IV) and BCl(g) (176.7 13) kJ-moP (Chapter VI) to give the selected enthalpy of formation for ZrCl(g), determined from the weighted average of the values obtained from Reaction (V.47) and (V.48) ... 

Horton, W. (1966) Statistical aspects of second and third law heats. Journal of Research of the National Bureau of Standards A, 70A, 533-539. 

Because it is necessary to exclude some substances, including some crystals, from the Nemst heat theorem, Lewis and Gibson (1920) introduced the concept of a perfect crystal and proposed the following modification as a definitive statement of the third law of themiodynamics (exact wording due to Lewis and Randall (1923)) ... 

Because of the Nemst heat theorem and the third law, standard themrodynamic tables usually do not report entropies of fomiation of compounds instead they report the molar entropy 50 7 for each element and... 

The variation of Cp for crystalline thiazole between 145 and 175°K reveals a marked inflection that has been attributed to a gain in molecular freedom within the crystal lattice. The heat capacity of the liquid phase varies nearly linearly with temperature to 310°K, at which temperature it rises more rapidly. This thermal behavior, which is not uncommon for nitrogen compounds, has been attributed to weak intermolecular association. The remarkable agreement of the third-law ideal-gas entropy at... 

Typically, the biggest lost that occurs in chemical processes is in the combustion step (6). One-third of the work potential of natural gas is lost when it is burned with unpreheated air. Eigure 3 shows a conventional and a second law heat balance. The conventional analysis only points to recovery of heat from the stack as an energy improvement. Second law analysis shows that other losses are much greater. 

As indicated earlier, when phase transitions occur, AS for the phase transition must be included in the Third Law calculation of the entropy. For example, Figure 4.4 summarizes the heat capacity of Nt as a function of temperature, up... 

This relationship led to an early formulation of the Third Law known as the Nernst heat theorem, which states that for any isothermal process... 

Experience indicates that the Third Law of Thermodynamics not only predicts that So — 0, but produces a potential to drive a substance to zero entropy at 0 Kelvin. Cooling a gas causes it to successively become more ordered. Phase changes to liquid and solid increase the order. Cooling through equilibrium solid phase transitions invariably results in evolution of heat and a decrease in entropy. A number of solids are disordered at higher temperatures, but the disorder decreases with cooling until perfect order is obtained. Exceptions are... 

C. C. Stephenson and W. F. Giauque. "A Test of the Third Law of Thermodynamics by Means of Two Crystalline Forms of Phosphine. The Heat Capacity. Heat of Vaporization and Vapor Pressure of Phosphine. Entropy of the Gas". J. Chem. Phys.. 5. 149-158 (1937). 

G. E. Gibson and W. F. Giauque. "The Third Law of Thermodynamics. Evidence from the Specific Heats of Glycerol that the Entropy of a Glass Exceeds that of a Crystal at the Absolute Zero". J. Am. Chem. Soc.. 45. 93-104 (1923). 

K. S. Pitzer and L. V. Coulter. "The Heat Capacities. Entropies and Heats of Solution of Anhydrous Sodium Sulfate and of Sodium Sulfate Decahydrate. The Application of the Third Law of Thermodynamics to Hydrated Crystals". J. Am. Chem. Soc.. 60. 1310-1313 (1938). 

One of the more interesting results of these calculations is the contribution to the heat capacity. Figure 10.10 shows the temperature dependence of this contribution to the heat capacity for CH3-CCU as calculated from Pitzer s tabulation with 7r = 5.25 x 10-47 kg m2 and VQ/R — 1493 K. The heat capacity increases initially, reaches a maximum near the value expected for an anharmonic oscillator, but then decreases asymptotically to the value of / expected for a free rotator as kT increases above Vo. The total entropy calculated for this molecule at 286.53 K is 318.86 J K l-mol l, which compares very favorably with the value of 318.94T 0.6 TK-1-mol 1 calculated from Third Law measurements.7... 

To calculate the entropy of a substance, we use Boltzmann s formula, but the calculations are sometimes very difficult and require a lot of manipulation of Eq. 6. To measure the entropy of a substance, we use the thermodynamic definition, Eq. 1, in combination with the third law of thermodynamics. Because the third law tells us that S(0) = 0 and Eq. 2 can be used to calculate the change in entropy as a substance is heated to the temperature of interest, we can write... 

The Heat of Formation of CF2. Several of experimental approaches have been used to determine AHf° (CF2).The most common technique involves mass spectrometric measurement of appearance potentials. The earlier appearance potential measurements indicated that A(CF2) = -30 10 kcal. mole 32), but it now appears this value is too high. Margrave and co-workers 33 reported a mass spectrometric study of the C2F4/CF2 equilibrium between 1127—1244 °K. Both second and third-law determinations of the enthalpy of reaction for C2F4 - 2 CF2 were made, yielding-39.3 3 kcal. mole 1 for A/fy-°298 (CF2, g). 

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