Standard enthalpy sublimation

Krypton Difluoride. Krypton difluoride [13773-81 -4] KrF is a colorless crystalline solid which can be sublimed under vacuum at 0°C but is thermodynamically unstable and slowly decomposes to the elements at ambient temperatures (Table 1). It can, however, be stored for indefinite periods of time at —78° C. The KrF molecule has been shown, like XeF2, to be linear in the gas phase, in the sofld state, and in solution. The standard enthalpy of... 

Use the information in Tables 6.3, 6.7, and 6.8 to estimate the enthalpy of formation of each of the following compounds in the liquid state. The standard enthalpy of sublimation of carbon is +717 kJ-moF 1. (a) H20 (b) methanol, CH,OH (c) benzene, C6H6 (without resonance) (d) benzene, C6H6 (with resonance). 

The values of AHf (g) carry both the experimental uncertainty in the standard enthalpy of formation of the crystalline (or liquid) metal compound and the uncertainty (experimental or estimated) in the enthalpy of sublimation (or vaporization). 

Table 9. Valence m.o. electron configuration Ofg e"g e%g, enthalpy of sublimation, AHSU, and standard enthalpy of formation, (AHf, g), of metallocenes. Mean bond dissociation enthalpy, D (M-Cp) (Refs.68 69 ) and (Metal-cyclopentadienyl ring) bond length, r(M-Cp). (Ref.72 ).

Table 14. Standard enthalpies of sublimation, formation and disruption and bond enthalpy contributions, iT(W-N) kJ mol-1, for N-donor complexes of tungsten W(CO)6 nLn]...

The enthalpy of reaction 2.45 cannot be determined directly. As shown in figure 2.5, it is calculated by using several experimental quantities the standard enthalpy of formation of the solid alkoxide, the standard sublimation enthalpy and the ionization energy of lithium, and the standard enthalpy of formation and the adiabatic electron affinity of gaseous methoxy radical (equation 2.47). 

The enthalpy of this process can be accurately calculated from literature data. The standard enthalpy of sublimation of iodine is known at 298.15 K (62.42 0.08 kJ mol-1 [58]), so we have (see section 2.4) ... 

The types of values reported in the database standard enthalpies of formation at 298.15 K and 0 K, bond dissociation energies or enthalpies (D) at any temperature, standard enthalpy of phase transition—fusion, vaporization, or sublimation—at 298.15 K, standard entropy at 298.15 K, standard heat capacity at 298.15 K, standard enthalpy differences between T and 298.15 K, proton affinity, ionization energy, appearance energy, and electron affinity. The absence of a check mark indicates that the data are not provided. However, that does not necessarily mean that they cannot be calculated from other quantities tabulated in the database. 

Standard Enthalpies, Entropies and Gibbs Free Energies of Sublimation of... 

We could calculate AH for this if we knew (for the elements) the enthalpy of formation of molecules from their atoms. Some crystalline elements (especially metals) vaporize as monatomic gases, and it is not too difficult to determine their heats of sublimation. Some elements—such as H2, 02, an( Br2—are diatomic gases that dissociate into atoms at high temperature these dissociation energies may also be determined. Table 14-1 also includes the standard enthalpies of formation of a number of atoms these are based on the normal physical form of the element at 25.0°C. For HC1 we find... 

Calculate the bond energies in the following gaseous molecules (a) CO, (b) C02, (c) S02, (d) NaCl Thc enthalpy of sublimation of NaCI is AH +54 70 kcal/mole, and the standard enthalpy of formation of NaClls, is A HI = -98 23 kcal/mole... 

A, H° Asub "° standard enthalpy of reaction per mole (reactants -x products) standard enthalpy of sublimation per mole A rH°... 

In order to be able to convert the standard enthalpies of formation Af//°(g) for the gas-phase into values for the condensed phase, for covalent molecules (NG) we additionally require the enthalpy of sublimation A//suh (for solids) or the enthalpy of vaporization AHvap (for liquids). Both values can be estimated using the Trou-ton s rule, in which Tm is the melting point of the solid and Tb is the boiling point of the liquid [25] ... 

Standard enthalpy of sublimation at 0°K. kcal./gram atom. For the gaseous phase units cal./(gram atom °K.). 

IMiysico-chemical properties were given by I. Noble and coAvorkers 2- 9. llie oxidizer properties by Prankel and co-workcrs (240). and heat of toimaiion by Apin. IVpekin and co-workers 24l. The standard enthalpy of formation was found to be 20.0 1 l.O kcal/inol, and in the gas phase 36.0 . 1.4 kcalfmol. The enthalpy of sublimation is 16.0 0.4 kcal/mol. 

Values of dissociation energies were taken with few exceptions from T. L. Cottrell, The Strength of Chemical Bonds , Butterworth, London (1958). Standard enthalpies of formation, heats of fusion and vaporization or heats of sublimation were taken from F. D. Rossini, D. D. Wagman, W. H. Evans, S. Levine and I. Jaffee, "Selected Values of Chemical Thermodynamic Properties , National Bureau of Standards Circular 500 (1952), except for cases where more recent data have been published since. Improved enthalpy data for a number of fluorides and chlorides have been compiled hy H. A. Skinner, Pure and Applied Chemistry 8, 113 (1964). Heats of atomization of the elements were taken from D. R. Stull and G. C. Sinke, Thermodynamic Properties of the Elements , Advances in Chemistry Series No. 18, American Chemical Society, Washington (1956). Enthalpy data for GeBr4 and... 

Values of the standard enthalpies of atomization, Aj,7/"(298 K), (or sublimation) in Table 5.2 refer to the processes defined in equation 5.2, and correspond to the destruction of the metallic lattice. Mercury is an exception, since at 298 K it is a liquid. 

I liysico-clieniical properties were given by P. N< blc and co-woikcrs 2. y. the oxidi/er prt perties by I ranKcl and co-woikcrs 240l.aiid heat of I oi mat ion by Apin. I epckiii and co-workers (2411. lire standard enthalpy r>f forinathtn was found to he 20.0 1.0 kcal/mol. and in the gas phase 36.0 1.4 kcal/inol. TI .c enthalpy ol sublim.ition is 16.9 t 0.4 kcal/mol. 

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