Enthalpy corrections

There are two enthalpy corrections for strongly associating vapors. The dominant term is due to the combined enthalpies of reaction of the stoichiometric species, Ah, to form the true... 

The total enthalpy correction due to chemical reactions is the sum of all the enthalpies of dimerization for each i-j pair multiplied by the mole fraction of dimer i-j. Since this gives the enthalpy correction for one mole of true species, we multiply this quantity by the ratio of the true number of moles to the stoichiometric number of moles. This gives... 

When the reduced temperature is iess than 0.85, d(T depends very little on pressure. Table 4.8 gives values for and for enthalpy correction factorsi calculated by the Lee and Kesler method. 

The sum of the energy collection for heating the molecule from 0 to 298 K plus RT is called the thermal enthalpy correction (TCH) and yields... 

A/i = enthalpy correction when barometric pressure differs from standard barometer, for saturated or unsaturated air, Btu/lb dry air V = volume of moist air, ftVlb dry air... 

Enthalpy data are given on the basis of kilojoules per kilogram of diy air. Entbalpy-at-saturation data are accurate only at the saturation temperature and humidity. Enthalpy deviation curves permit enthalpy corrections for humidities less than saturation and show how the wet-bulb-temperature hues do not precisely coincide with constant-enthalpy, adiabatic cooling hnes. 

Binary minimum reflux so calculated implies feed enthalpy just equal to the above started vapor V and liquid L. Any increase or decrease in that enthalpy must be matehed by inerease or decrease in total heat content of overhead reflux. Note that the Underwood" binary reflux equation essentially computes the flash versus specifi-eation composition relationship along with enthalpy correction. 

These values predict a value of -34.0 kcal moT for AH . This value is in excellent agreement with experiment (-34.0 2.0 kcal mol). Note that we didn t need to run a frequency job on Li, but rather computed the enthalpy correction as 2 RT (just a translational component). 

Table 3 contains the enthalpies, zero point energies, entropies and free enthalpies of the activation and reaction steps (3)—(5). The enthalpies are the pure differences of the enthalpies of formation calculated by MINDO/3 at T = 298 K in the gas phase. The free enthalpies were calculated with the help of enthalpies corrected by the zero point energies and of the entropies given in Table 3. 

Example 9.2 Apply the enthalpy correction to the prediction of minimum reflux ratio for Example 9.1 to obtain a more accurate estimate of the minimum reflux ratio. 

III parentheses, relative free enthalpies corrected for statistical weights. CFF calculates another conformer, AAG, as the global minimum see text. 

Indeed, we can make use of either liquid- or gaseous-phase enthalpies of formation despite our prejudice for the latter because we may invoke a constant 14 kJ mol1 SAHw differential vaporization enthalpy correction to the former80. That is, should some enthalpy of vaporization be unavailable from experiment, we invoke the simple, approximate, equations 29 and 30 ... 

With temperature, entropy, and enthalpy correction, they obtained free energy change AG°. The reversible electrochemical potential was calculated by the equation... 

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