Ideal Gas Thermodynamic Properties of Eight Chloro- and Fluoromethanes

Abstract

The structural data, vibrational assignments, enthalpies of vaporization and formation for chloromethane, dichloromethane, trichloromethane, tetrachloromethane, fluoromethane, difluoromethane, trifluoromethane, and tetrafluoromethane were critically reviewed_ Based on the selected best values, the thermodynamic properties for each of these eight chloro-and fluoromethanes were calculated by statistical thermodynamic methods using the rigid-rotor harmonic-oscillator approximations. The derived entropies and heat capacities are compared with the available third law entropies and vapor heat capacities. The calculated values of C~, So, and l:!.Hr at 298.15 and 700 K are compared with those reported in the other major compilations.

Kinetics of the gas‐phase reaction CH3F + I2 ⇆ CH2FI + HI: The CH bond dissociation energy in methyl and methylene fluorides

“…Pritchard, Bryant, and Thommarson [16] have measured the relative rates of reactions (6) and (7) and obtained reproducible results in the temperature range of 475-575 K, but experienced difficulty at lower temperatures. In this higher range they The entropies and heat capacities of CF2H2 [12], CH4 [ll], and CH3 [18] are well known, and these data may be reliably estimated for CHF2 using bond subtractivity [19]. Thus So(CHF2, g, 500 K) = 67.2 kcal/mol, which leads to AS; (500 K) = 0.0 and = 1.0 cal/mol.K from 500 to 300 K. Using these data, one calculates that AH; (500 K) = 2.07 and AH; (298 K) = 1.87 kcal/mol.…”

“…f l kcal/mol) is a reasonable assessment of the reliability of this result, so that DHO(CHF2-H) = 103.2 f 1 kcal/mol. This yields [12], AH;(CHF2, g, 298 K) = -57.1 f 1 kcal/mol. With the results obtained here and the data in [12,15, and 191, we can calculate the C-H and C-F bond dissociation energies for all the fluoromethanes, and these data are summarized in Table 111.…”

“…The bond dissociation energies for the C-C1 bond are summarized in Table IV and show an increase in bond energy with increasing a-fluorine substitution. There is, however, no effect on the C-Br bond [22] (due either to the decrease [12]. From [20].…”

“…A t the mean temperature of 666 K, the observed activation energy E4 = 30.8 f 0.2 kcal/mol may be -combined with the established assumption [5], E3 = 1 f 1 kcal/mol, and AC, = -0.65 cal/K-mol, obtained from group additivity [lo], to yield Further, AHj(CH3F, g, 298 K) = -56.8 f 2 kcal/mol [12], so that eq. (V) yields AH;(CH2F, g, 298 K) = -7.6 f 2 kcal/mol.…”

“…All reactions were monitored spectrophotometrically using equipment described elsewhere [9]. At each reaction temperature, the specific absorption coefficients of 12 and HI were determined from Beer's law plots taken at 500 and 255 nm, respectively.…”