Molar entropy of vaporization

Por most normal liquids the constant has a value of approx. 88JmolK" . Associated liquids show marked variations from this value. The Trouton constant is the molar entropy of vaporization. 

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. 

Calculate the molar entropy of vaporization for liquid hydrogen iodide at its boiling point,... 

Related Calculations, This procedure can be used to obtain the entropy of phase change for any compound. If heat-of-vaporization data are not available, the molar entropy of vaporization for nonpolar liquids can be estimated via an empirical equation of Kistyakowsky ... 

Like water, almost all substances can be in the three common states of matter. Table 5 lists the molar enthalpies and entropies of fusion and vaporization for some elements and compounds. Because intermolecular forces are not significant in the gaseous state, most substances have similar values for molar entropy of vaporization, ASy p-... 

In other words, the boiling point of a liquid, Tbp, is equal to molar enthalpy of vaporization, AHyap, divided by molar entropy of vaporization, ASyap. 

Remarkably, most liquids have similar values for the molar entropy of vaporization. Trouton s rule summarizes this observation ... 

Ethanol (CH3CH2OH) has a normal boiling point of 78.4°C and a molar enthalpy of vaporization of 38.74 kj mol Calculate the molar entropy of vaporization of ethanol and compare it with the prediction of Trouton s rule. 

Here, ASy is the molar entropy of vaporization. Equation (6.85) seems to be closely related to the ebullioscopy law and the law emerging in vapor pressure osmometry. Note that the way of derivation here runs via Raoulfs law and the Clausius - Clapeyron equation, whereas ebullioscopy is derived usually via the chemical potential. Moreover, recalling van l Hoff s law of osmometry, UV = X2RT, we can relate Eq. (6.85) easily to osmometry, arriving at... 

If the molar entropy of vaporization can be treated as a constant, as Trouton s rule suggests, then the relative elevation of the boiling point, AT/T, is universally related to the mole fraction X2 according to Eq. (6.85). 

Trouton s rule states that for many liquids at their normal boiling points, the standard molar entropy of vaporization is about 88 I/mol-K. (a) Estimate the normal boiling point of bromine, Br2, by determining AH for Br2 using data from Appendix C. Assume that AHJ p remains constant with temperature and that Trouton s rule holds, (b) Look up the normal boiling point of Br2 in a chemistry handbook or at the WebElements Web site (www.webelements.com). 

Most liquids follow Trouton s rule, which states that the molar entropy of vaporization lies in the range of 88 5 J/mol-K. The normal boiling points and enthalpies of vaporization of several organic liquids are as follows ... 

The Normal Boiling Point (Tb), Molar Enthalpies of Vaporization, XHap) and Molar Entropy of Vaporization (AS ,ap) of Severai Substances. 

The subscripts in the list above are also used for other molar transition quantities. Thus, there is the molar entropy of vaporization Ayap5, the molar internal energy of sublimation Asubf. and so on. 

Similarly, if the conversion of a liquid to vapor occurs at a constant pressure at its boiling point Tboii, then the molar entropy of vaporization A5vap and the molar enthalpy of vaporization A/7vap are related by... 

In this expression, is the molar entropy of vaporization and B is the second virial coefficient of the solvent Q and the homologous alkane ( ). The temperature derivative of B compensates for possible association of the solvent molecules in the vapor phase. The dimensionless values of AAS (T,P°)/R from [27] are shown in Table 3.8 for the solvents dealt with here, but for some of them, the values of dBJdT are not known these solvents are not expected to associate in the vapor phase anyway. For solvents for which the value of AAS T, P°)/R has not been previously determined, the values of AS (T, P°) and AS (T, P°) are obtained for 25 C from ... 

A useful generalization known as Trouton s rule states that for many liquids at their normal boiling points, the standard molar entropy of vaporization has a value of about 87 J moH K . ... 

PRACTICE EXAMPLE A What is the standard molar entropy of vaporization, AyapS°, for CCI2F2, a chlorofluorocarbon that once was heavily used in refrigeration systems Its normal boiling point is —29.79 °C, and AvapH° = 20.2 kJ mo - ... 

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