Standard enthalpy, 95 table

Themiodynamic tables usually report at least tln-ee quantities almost invariably the standard enthalpy of fomration at 298 K, Af (298 K) usually the standard entropy at 298 K,, S (298 K) (not AS y298 K), but the... 

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... 

Table 1.5. Standard Enthalpies of Formation of Some Hydrocarbons (kcal/mol) ...

The standard enthalpies of formation of ions in aqueous solution listed at the bottom of Table 8.3 are relative values, established by taking... 

Table 4.3 summarizes values taken from the JANAF tables for the Gibbs free energy functions and standard enthalpies of formation for a few common substances. The JANAF tables provide a more complete tabulation. 

Extensive tabulations of standard enthalpies of formation and related thermodynamic data can be found in the literature.5 Table 9.1 summarizes selected values from these sources. 

TABLE 6.3 Substance Standard Enthalpies pf Physical Change Freezing Formula point (I<) (kj-rnpl ) Boiling point (K) AHV P° (kj-mol )... 

TABLE 6.4 Substance Standard Enthalpies of Combustion at 25°C (kl-mol ) Formula AH°... 

Standard enthalpies of combustion are listed in Table 6.4 and Appendix 2A. We have seen in Toolbox 6.1 how to use enthalpies of combustion to obtain the standard enthalpies of reactions. Here we consider another practical application— the choice of a fuel. For example, suppose we want to know the heat output from the combustion of 150. g of methane. The thermochemical equation allows us to write the following relation... 

The standard enthalpy of formation of diamond is therefore reported as AHt°(C, diamond) = + 1.9 kj-mol l. Values for a selection of other substances are listed in Table 6.5 and Appendix 2A. 

Self-Test 6.16A Calculate the standard enthalpy of formation of ethyne, the fuel used in oxyacetylene welding torches, from the information in Tables 6.4 and 6.5. 

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). 

SOLUTION The boiling point corresponds to 329.4 K, and we note from Table 6.3 that the standard enthalpy of vaporization of acetone at its boiling point is 29.1 kj-mol Therefore,... 

Standard Gibbs free energies of formation can be determined in various ways. One straightforward way is to combine standard enthalpy and entropy data from tables such as Tables 6.5 and 7.3. A list of values for several common substances is given in Table 7.7, and a more extensive one appears in Appendix 2A. 

STRATEGY We write the chemical equation for the formation of HI(g) and calculate the standard Gibbs free energy of reaction from AG° = AH° — TAS°. It is best to write the equation with a stoichiometric coefficient of 1 for the compound of interest, because then AG° = AGf°. The standard enthalpy of formation is found in Appendix 2A. The standard reaction entropy is found as shown in Example 7.9, by using the data from Table 7.3 or Appendix 2A. 

TABLE 7.2 Standard Enthalpies and Gibbs Free Energies of Formation (Values are joules per mole of the substance formed)... 

Table 1.3 Esti mated values of the four components of the contribution made by ligand field stabilization energy to the lattice enthalpy of KsCuFe, to the hydration enthalpy of Ni (aq), AH (Ni, g), and to the standard enthalpy change of reaction 13.

The third law of thermodynamics establishes a starting point for entropies. At 0 K, any pure perfect crystal is completely constrained and has S = 0 J / K. At any higher temperature, the substance has a positive entropy that depends on the conditions. The molar entropies of many pure substances have been measured at standard thermodynamic conditions, P ° = 1 bar. The same thermodynamic tables that list standard enthalpies of formation usually also list standard molar entropies, designated S °, fbr T — 298 K. Table 14-2 lists representative values of S to give you an idea of the magnitudes of absolute entropies. Appendix D contains a more extensive list. 

Unfortunately, the above thermodynamic approach has only been followed for two systems, namely As-Pt(lll) and Bi-Pt(lll) [Blais et al., 2001, 2002]. Table 7.3 summarizes the main results. Thermodynamic data about the bulk formation of As(OH)s and Bi(OH)2 are not available for comparison. The only data available is the standard enthalpy for the bulk formation of Bi(OH)3 (A/7 = 711.3kJ/mol). 

When one considers the potential high-energy release on rupture of a carborane unit, together with the thermodynamic stability of combustion products, it is hardly surprising that there is a body of literature that reports on the use of carbo-ranes within propellant compositions. Their use in energetic applications is to be expected when the enthalpy of formation (AH/) data for the products of combustion for boron are compared to those of carbon. Thermodynamic data for the enthalpy of formation of o-carborane and of typical boron and carbon combustion products is shown in Table 4. Measurements of the standard enthalpy of combustion32 for crystalline samples of ortho-carborane show that complete combustion is a highly exothermic reaction, AH = — 8994 KJmol. ... 

The enthalpy change for the reaction is given by the difference in the standard enthalpies of formation of the species, which can be found from the table in Appendix C ... 

TABLE 1. Standard enthalpies of formation of organogermanium compounds (kJmol -i)a... 

TABLE 6. Standard enthalpies of formation of organolead compounds (kJ mol 1)... 

The enthalpy that accompanies a change of physical state at standard conditions is called the standard enthalpy of transition and is denoted A trsH°. Enthalpy changes accompanying chemical reactions at standard conditions are in general termed standard enthalpies of reaction and denoted A r H0. Two simple examples are given in Table 1.3. In general, from the first law, the standard enthalpy of a reaction is given by... 

Table 10.4 Selected experimental determinations of the standard enthalpy of formation of LaNi5 at 298.15 K.

We define the standard enthalpy of formation AH as the enthalpy change involved in forming 1 mol of a compound from its elements, each element existing in its standard form. Both T and p need to be specified, because both variables influence the magnitude of AH. Most books and tables cite AH at standard pressure p and at a temperature of 298 K. Table 3.1 cites a few representative values of AH. ... 

Table 3.2 Standard enthalpies of combustion A7/c° for a few organic compounds (all values are at 298 K)...

SAQ 3.9 Calculate the standard enthalpy of combustion A He for burning S-D-glucose, C6Hi206. The required values of AHf may be found in Table 3.1. 

Table 1. Standard enthalpy of formation of metal carbonyls [Mm(CO) ] in the gas phase. Bond description and bond enthalpy contributions (T, M and B) to the enthalpy of disruption, AHq...

Table 3. Standard enthalpy of formation of the gaseous metal atom, A/ff (M, g), coordina-tion number n of the atom in the bulk metal at room temperature and values of M and T calculated by equations 1 and 3. Thermochemical values in kj mol-1...

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 12a. Standard enthalpy of formation, A/ff(g), enthalpy of disruption, AHjy, and metal-halogen bond enthalpy contribution, (M-X), in metal carbonyl halides (kJ mol-1)...

The standard enthalpies of formation of the gaseous compounds and the enthalpy of disruption derived therefrom are given in Table 13. An interesting problem arises as to how these results are to be evaluated. If the value of AHf [M(CO)s, g] derived15,1 ) from electron impact measurements on M2(CO)io (M = Mn, Re) is used, then as outlined earlier this will be expected to give an upper limit to the value of D(M-M). It has been shown16) that for all values of Z)(M-M) below specified upper limits the following relation holds... 

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