Vaporization standard enthalpy

Enthalpies are referred to the ideal vapor. The enthalpy of the real vapor is found from zero-pressure heat capacities and from the virial equation of state for non-associated species or, for vapors containing highly dimerized vapors (e.g. organic acids), from the chemical theory of vapor imperfections, as discussed in Chapter 3. For pure components, liquid-phase enthalpies (relative to the ideal vapor) are found from differentiation of the zero-pressure standard-state fugacities these, in turn, are determined from vapor-pressure data, from vapor-phase corrections and liquid-phase densities. If good experimental data are used to determine the standard-state fugacity, the derivative gives enthalpies of liquids to nearly the same precision as that obtained with calorimetric data, and provides reliable heats of vaporization. 

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,... 

Self-Test 7.7A Use Trouton s rule to estimate the standard enthalpy of vaporization of liquid bromine, which boils at 59°C. 

The standard entropy of vaporization of benzene is approximately 85 J-K -mol-1 at its boiling point, (a) Estimate the standard enthalpy of vaporization of benzene at its normal boiling point of 80.°C. (b) What is the standard entropy change of the surroundings when 10. g of benzene, CfiHfi, vaporizes at its normal boiling point ... 

At this point we can use AGvap° = AHvap° — TAS °, where AHrap° and ASvap° are the standard enthalpy and entropy of vaporization, respectively, and obtain... 

Self-Test 8.2A The vapor pressure of water at 25°C is 23.76 Torr and its standard enthalpy of vaporization at that temperature is 44.0 kj-mol-1. Estimate the vapor pressure of water at 35°C. 

C. Using these data, calculate (a) the standard enthalpy of vaporization (b) the standard entropy of vaporization ... 

The vapor pressure of chlorine dioxide, Cl02, is 155 Torr at —22.75°C and 485 Torr at ().()0°C. Calculate (a) the standard enthalpy of vaporization (b) the standard entropy of vaporization (c) the standard Gibbs free energy of vaporization (d) the normal boiling point of C102. 

It is standard practice in chemical laboratories to distill high-boiling-point substances under reduced pressure. Trichloroacetic acid has a standard enthalpy of vaporization of 57.814 kj-mol 1 and a standard entropy of vaporization of 124 J-K 1-mol. Use this information to determine the pressure that one would need to achieve to distill trichloroacetic-acid at 80.°C. 

Ha Hi AHr AH m AH°fi AHS, AHvaP A I see Dimensionless Groups Henry s law constant for species Pa m3 mol-1, equation 9.2-8 enthalpy of reaction for reaction as written, J standard enthalpy of reaction, J standard enthalpy of combustion of species i J mol-1 standard enthalpy of formation of species i, J mol-1 standard molar enthalpy of reaction with respect to species i, J mol-1 enthalpy of vaporization, J mol-1 standard molar enthalpy of activation (TST), J mol-1 initiator (species) inhibitor, inert species... 

Figure 1.3 Standard enthalpy of aluminium relative to 0 K. The standard enthalpy of fusion (Afugffm) is significantly smaller than the standard enthalpy of vaporization (A vap// ).

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). 

As mentioned, AvapH refers to 326 K and to 7848 Pa, that is, the calculated value is not the standard enthalpy of vaporization. The correction to the standard states (at 326 K) could be estimated with equation 2.16, but there are more... 

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. 

Table XI gives the room-temperature, atmospheric pressure crystal structures, densities, and atomic volumes, along with the melting points and standard enthalpies of vaporization (cohesive energies), for the actinide metals. These particular physical properties have been chosen as those of concern to the preparative chemist who wishes to prepare an actinide metal and then characterize it via X-ray powder diffraction. The numerical values have been selected from the literature by the authors.

Table 6.3 Experimental Standard Enthalpies of Vaporization (AvapH,) and Standard Enthalpies of Transfer from Water to Air (Aaw//,) of Selected Organic Compounds at 25 °C ... 

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