Enthalpy standard molar list

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. 

Some standard molar enthalpies of formation are listed in Table 5.3. Notice that the standard enthalpies of formation of most compounds are negative. Thus, most compounds are more stable than the elements they are made from. 

Enthalpy of Formation. Tables of enthalpies of reaction generally list the enthalpies of formation of various compounds in their standard states from the elements in their standard states at the specified temperature. Thus, if the standard molar enthalpy of formation, Af//, of CO2 at 25°C is given as —393.509 kJ mol , the following equation is implied ... 

By applying equation 9.97 to plots of the type shown in figure 9.15B, Lux (1987) obtained standard molar enthalpies AH° and standard molar entropies ASf of solution of noble gases in melts, as listed in table 9.8. Enthalpies of solution are positive but close to zero, within error approximation. 

The symbol r indicates reaction in general. In particular cases r can be replaced by another appropriate subscript, e.g. A fH denotes the standard molar enthalpy of formation see p.51 below for a list of subscripts. 

The standard molar enthalpy of formation, AHf, listed in Appendix K is zero for almost all elements. A few entries are not zero explain why, and give two examples. 

The simple idea is that the amount of energy released during combustion depends on the strength of the bond in the gas. Euels with many weak (less stable) bonds such as C-C and C-H yield more energy than fuels with fewer such bonds or fuels that contain large numbers of strong bonds, e.g., C-0 and 0-H. Table 9.1 lists the standard molar enthalpies of combustion for a range of hydrocarbons. 

Entropies calculated using Equ on S 21 (with phase transitions) are called third-law (or) entropies because these values are not measured relative to some reference state. Third-law entropies per mole of material measured at the standard pressure of 1 bar are referred to as standard molar entropies, denoted by S°. Table 8.2 lists standard molar entropies for a variety of inorganic and organic substances— values for many other substances are given in Appendix 2. The units of S° are J mol K , in contrast to A ff values, which are generally given in kJ mol". Entropies of elements and compounds are all positive (that is, 5° > 0) for all T > 0 K. By contrast, the standard enthalpy of formation (AHf) for elements in their stable form is arbitrarily set equal to zero, and for compounds it may be positive or negative. 

PRACTICE EXAMPLE B A handbook lists the standard enthalpy of combustion of gaseous dimethyl ether, (CH3)20(g), at 298.15 K as -31.70 kj/g. What is the standard molar enthalpy of formation of dimethyl ether at... 

The computer subroutines for calculation of vapor-phase and liquid-phase fugacity (activity) coefficients, reference fugac-ities, and molar enthalpies, as well as vapor-liquid and liquid-liquid equilibrium ratios, are described and listed in this Appendix. These are source routines written in American National Standard FORTRAN (FORTRAN IV), ANSI X3.9-1978, and, as such, should be compatible with most computer systems with FORTRAN IV compilers. Approximate storage requirements and CDC 6400 execution times for these subroutines are given in Appendix J. 

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. 

Standard partial molar free enthalpies, enthalpies, and entropies of vaporization from infinitely dilute solutions in Apiezon M were calculated from retention volumes determined over a range of temperatures data are listed for many organic and a few MR4 compounds (M = Si, Ge, and Sn), including Ge(C2H5)4 [29]. Apiezon L and two polar stationary phases were used in similar studies on a variety of MRr,R4 n compounds, yielding relative molar enthalpies and entropies of solution at 100°C referred to Si(CH3)4 as the standard [43]. Retention volumes and heats of solutions on two stationary phases have also been compared for M(C2H5)4 and M(C2H5)3H compounds with M = Si, Ge, and Sn [38]. 

The experimental enthalpies of mixing and the related quantities are summarised in Table I. The values of s were 4666 and 5243 for a-CD and 3-CD systems,respectively. The experimental enthalpies of transfer were determined by the method mentioned above and the molar values of them are listed in Table I. From these experimental values of r m sis a function of / A p m°°, max, and K were determined by the successive approximation to K with least squares calculations. Residuals of Atr m(obs) over the Atr m(calc) are given in the last column of Table I and the standard deviations s are given in Table II as well as A p, and 2/max relative values of the enthalpies of transfer A plotted against /in Fig.2,where the solid lines are the smoothed values obtained. Agreements between them are good. The molar enthalpies of inclusion determined for the present systems are listed in Table III as well as those determined earlier. 

Standard tables of first-year chemistry texts make contact with the molecular scale by listing standard free energies and enthalpies of formation, and molar entropies ... 

The second characteristic concerns standard tables. These provide indispensable data for the chemist regarding molar entropies, enthalpies, free energies, and ABA energies. Concerning information, the tables can be augmented by applying the methods of the previous section. Table 6.1 lists familiar... 

Standard enthalpies of formation from oxides (A,JT°) and from elements H°), and partial molar enthalpy of oxygen, evaluated for 298 K and the listed exact compositions, according to drop-calorimetry for units see the... 

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