Chlorine standard entropies

The standard entropy change for the atom-molecule reactions is in the range 5-20 mole and the halogen molecule dissociation has an eiiU opy change of about 105 e.u. The halogen molecule dissociation energy decreases from chlorine to iodine, but the atom-molecule reactions become more endothermic from chlorine to iodine, and this latter effect probably influences the relative contributions to the mechanism from chain reaction and biinolecular reaction. 

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. 

Problem Calculate the standard entropy of atomic chlorine at 25 C. 

Consider the reaction of chlorine with methane, in which two molecules react to give two molecules of product. For this reaction, = +2.9 J mole deg . The standard entropy change is a small value because the numbers of moles of reactant and products are equal. The TAS° term at 298 K is —860 J mole deg . Since AH° is —102 kj mole , AG° is —103 kj mole ... 

This table lists standard enthalpies of formation AH°, standard third-law entropies S°, standard free energies of formation AG°, and molar heat capacities at constant pressure, Cp, for a variety of substances, all at 25 C (298.15 K) and 1 atm. The table proceeds from the left side to the right side of the periodic table. Binary compounds are listed under the element that occurs to the left in the periodic table, except that binary oxides and hydrides are listed with the other element. Thus, KCl is listed with potassium and its compounds, but CIO2 is listed with chlorine and its compounds. 

Rubber Company Handbook (Weast, 1987) is one of the more commonly available sources. More complete sources, including some with data for a range of temperatures, are listed in the references at the end of the chapter. Note that many tabulations still represent these energy functions in calories and that it may be necessary to make the conversion to Joules (1 cal = 4.1840J). Because of the definition of the energy of formation, elements in their standard state (carbon as graphite, chlorine as CI2 gas at one bar, bromine as Br2 liquid, etc.) have free energies and enthalpies of formation equal to zero. If needed, the absolute entropies of substances (from which AS may be evaluated) are also available in standard sources. 

Another valuable source is the thermochemical property database assembled by Burcat and Ruscic [29], which is available online at ftp // ftp.technion.ac.il/pub/supported/aetdd/thermodynamics/. This collection is regularly updated by Prof. Burcat. It contains data for 1500 species, presented in the form of polynomial coefficients that can be used to compute the enthalpy, entropy, and heat capacity as a function of temperature. While Burcat s tables include a number of aluminum-oxygen compounds, they do not happen to include the aluminum-chlorine species that we have been using as an example. Of course, there are many other handbooks and compilations of thermodynamic properties. However, the vast majority of these focus on organic compounds and/or condensed phase species. Standard handbooks, such as the CRC Handbook of Chemistry and Physics, rarely have any information not included in the sources cited above. 

The National Bureau of Standards Report 6928 lists the properties of compounds of lithium, beryllium, magnesium, and aluminium with hydrogen, oxygen, fluorine, chlorine, nitrogen, and carbon. Thermodynamic functions for the ideal gases, solids, and liquids are tabulated (e.g. values of free energy functions and enthalpy functions , entropy, and heat capacity). 

Problem For the cell reaction of hydrogen gas and chlorine gas to produce HCl in aqueous solution (dissociated into ions), how does temperature affect the cell voltage given that the standard state molar entropy for the products is 56.3 J moH ... 

---