Enthalpy calculations vapor

Table 1 indicates that the enthalpy of mixing in the liquid phase is not important when calculating enthalpies of vaporization, even though for this system, the enthalpy of mixing is large (Brown, 1964) when compared to other enthalpies of mixing for typical mixtures of nonelectrolytes. 

Finally, Table 2 shows enthalpy calculations for the system nitrogen-water at 100 atm. in the range 313.5-584.7°K. [See also Figure (4-13).] The mole fraction of nitrogen in the liquid phase is small throughout, but that in the vapor phase varies from essentially unity at the low-temperature end to zero at the high-temperature end. In the liquid phase, the enthalpy is determined primarily by the temperature, but in the vapor phase it is determined by both temperature and composition. 

The computation of pure-component and mixture enthalpies is implemented by FORTRAN IV subroutine ENTH, which evaluates the liquid- or vapor-phase molar enthalpy for a system of up to 20 components at specified temperature, pressure, and composition. The enthalpies calculated are in J/mol referred to the ideal gas at 300°K. Liquid enthalpies can be determined either with... 

This chapter presents quantitative methods for calculation of enthalpies of vapor-phase and liquid-phase mixtures. These methods rely primarily on pure-component data, in particular ideal-vapor heat capacities and vapor-pressure data, both as functions of temperature. Vapor-phase corrections for nonideality are usually relatively small. Liquid-phase excess enthalpies are also usually not important. As indicated in Chapter 4, for mixtures containing noncondensable components, we restrict attention to liquid solutions which are dilute with respect to all noncondensable components. 

ENTH calculates vapor or liquid enthalpies, J/mole, (reference, ideal gas at 300 K) for a mixture of N components (N <... 

ENTH CALCULATES VAPOR OR LIQUID ENTHALPIES (REF IDEAL GAS AT 300 K1 H... 

Selected physical properties are given in Table 1 and some thermodynamic properties in Table 2. Vapor pressure (P) and enthalpy of vaporization (H) over the temperature range 178.45 to 508.2 K can be calculated with an error of less than 3% from the following equations wherein the units are P, kPa Pi, mj/ mol T, K and = reduced temperature, T/ T (1) ... 

Tbe enthalpy of vaporization decreases with temperature and is zero at tbe critical point. If tbe value of an enthalpy of vaporization AH is known at temperature T, this temperature dependency can be represented by tbe Watson relation to calculate another enthalpy of vaporization AH at any other temperature To ... 

Equations for calculating enthalpy of vapor of each component as a function of temperature... 

E6.2 The fugacity of liquid water at 298.15 K is approximately 3,17 kPa. Take the ideal enthalpy of vaporization of water as 43.720 TmoD1, and calculate the fugacity of liquid water at 300 K. 

J-K Frnol 1 and that of gaseous methanol is 43.89 J-K.-1 -mol, calculate the enthalpy of vaporization of methanol at its boiling point (64.7°C). (c) Compare the value obtained in part (b) with that found in Table 6.3. What is the source of difference between these values ... 

The heat capacity of liquid iodine is 80.7 J-K -mol, and the enthalpy of vaporization of iodine is 41.96 kj-mol 1 at its boiling point (184.3°C). Using these facts and information in Appendix 2A, calculate the enthalpy of fusion of iodine at 25°C. 

Self-Test 7.14A Calculate the entropy change of the surroundings when 1.00 mol H20(l) vaporizes at 90°C and I bar. Take the enthalpy of vaporization of water as 40.7 kj-mol. ... 

A note on good practice F.xponential functions are very sensitive to rounding errors, so it is important to carry out the numerical calculation in one step. A common error is to forget to express the enthalpy of vaporization in joules (not kilojoules) per mole, but keeping track of units will help you to avoid that mistake. 

The calculated boiling point corresponds to 77°C the experimental value is 78°C. The small error probably comes from assuming that the enthalpy of vaporization is a constant over the temperature range of the question and assuming that the vapor behaves like an ideal gas. 

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. 

C08-0076. Calculate the overall energy change for the formation of lithium fluoride from lithium metal and fluorine gas. hi addition to data found in Appendix C and Table 8-4. the following information is needed The bond energy of F2 is 155 kJ/mol, and lithium s enthalpy of vaporization is 159.3 kJ/mol. 

C14-0051. Table lists molar enthalpies of vaporization of several substances. Calculate the molar entropy of vaporization at its normal boiling point for each of the following (a) molecular oxygen (b) ethane (c) benzene and (d) mercury. 

The desired enthalpy of formation of 6,6-dimethylfulvene was determined by Roth citing measurement of hydrogenation enthalpies, and chronicled by Pedley citing enthalpies of combustion and vaporization. The two results differ by 7 kJ mol-1. We have opted for Roth s value because it is in better agreement with a value calculated using Roth s force field method. It is also to be noted that measurement cited by Pedley for the neat condensed phase could be flawed by the presence of partially polymerized fulvene and neither elemental abundance of the compound nor analysis of the combustion products would have disclosed this. Likewise, the measured enthalpy of vaporization would not have necessarily uncovered this contaminant. 

These energies relate to bond rearrangement in gaseous molecules, but calculations are often performed for reactions of condensed phases, by combining the enthalpies of vaporization, sublimation, etc. We can calculate a value without further correction if a crude value of AHr is sufficient, or we do not know the enthalpies of phase changes. 

One of the critical issues in vapor pressure methods is the choice of the procedure to calculate the vaporization enthalpy. For instance, consider the vapor pressures of ethanol at several temperatures in the range 309-343 K, obtained with a differential ebulliometer [40]. The simplest way of deriving an enthalpy of vaporization from the curve shown in figure 2.4 is by fitting those data with the integrated form of the Clausius-Clapeyron equation [1] ... 

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... 

Additional equations include physical property relationships to get densities and enthalpies, a vapor hydraulic equation to calculate vapor flow rates from known tray pressure drops, and a liquid hydraulic relationship to get liquid flow... 

Three peroxides with aromatic substituents have reported enthalpy of vaporization data, all from the same source". The enthalpies of vaporization of cumyl hydroperoxide and ferf-butyl cumyl peroxide are the same, which makes us skeptical of at least one of these values. The calculated b value for cumyl hydroperoxide is 31.5, consistent with the alkyl hydroperoxides. The calculated b value for tert-butyl cumyl peroxide is 15.4 and more than twice that for the mean of the dialkyl peroxides. The structurally related tert-butyl p-isopropylcumyl peroxide has a b value of 8.8 and so is consistent with the other disubstituted peroxides. 

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