1. Table 4. Parameters of the Cox Equation.
Tb Ao A1 106A2
tetradecane
pentadecane
hexadecane
heptadecane
octadecane
nonadecane
eicosane
Cox Equation
ln (p/po) = (1-Tb/T)exp(Ao +A1T +A2T 2)

2. ln(1/ta) = gslnHm(Tm)/R + intercept

3. If the vaporization enthalpy correlates with the enthalpy of transfer from solution to vapor, will the vapor pressure correlate with the vapor pressure of the solute on the stationary phase of the column?

4. The correlation observed between ln(1/ta) calculated by extrapolation to K using the equations given in the previous table and ln(p/po) at K calculated from the Cox equation for n-C14 to n-C20. The term po represents the vapor pressure ( kPa) at the reference temperature, Tb, the normal boiling point of the n-alkane; the equation of the line obtained by a linear regression is given by ln(p/po) = (1.26  0.01)ln(1/ta) – (1.718  0.048); r2 =

5. The selection of temperature is arbitrary, therefore this correlation should apply at any temperature.
Can these correlations be used to evaluate vapor pressures and vaporization enthalpies of the larger n-alkanes for which data is not presently available?
Until recently vaporization enthalpies and vapor pressures were available up to eicosane.

6. Why is there any interest in knowing the vapor pressures and vaporization enthalpies of these higher alkanes?
1. n-Alkanes serve as excellent standards for the evaluation of vaporization enthalpies and vapor pressures of other hydrocarbons.
2. The properties of the n-alkanes are useful in predicting properties of crude oil and useful in the development of models for handling petroleum.

7. Suppose a mixture of the following n-alkanes were analyzed by gas chromatography:
Retention Times for C17 to C23
T/K
t/min
methylene chloride
heptadecane
octadecane
nonadecane
eicosane
heneicosane
docosane
tricosane

8. A plot of ln(1/ta) vs 1/T results in
C17 to C23.
Tm = K slngHm/R intercept r2
heptadecane  
octadecane  
nonadecane  
eicosane  
heneicosane  
docosane  
tricosane  

9. slngHm(508 K) lgHm (298.15 K) lgHm (298.15 K)
C17 to C23
slngHm(508 K) lgHm ( K) lgHm ( K)
(lit) (calc)
heptadecane 2.
octadecane 2.2
nonadecane 2.3
eicosane 2.4
heneicosane 2.5
docosane 2.7
tricosane 2.8
lgHm ( K) = (1.570.04) slngHm(Tm) – (6.660.30); r2 =

10. Figure. The correlations obtained by plotting vaporization enthalpy at T = K against the enthalpy of transfer measured at the mean temperature indicated; triangles: n-C14 to C20 (449 K); solid triangles: n-C17 to C23(508.8 K); hexagons: n-C19 to C25(538.7 K); squares: n-C21 to C27(523.8 K); circles: n-C23 to C30(544 K).

11. In this manner, vaporization enthalpies and vapor pressures were calculated from T = 570 to K for C21 to C38.
All of the compounds are solids at T = K so the vapor pressures and vaporization enthalpies are hypothetical properties.
Chickos, J. S.; Hanshaw, W. J. Chem. Eng. Data 2004, 49, 77-85
Chickos, J. S.; Hanshaw, W. J. Chem. Eng. Data 2004, in press.

12. Figure. The vaporization enthalpies of the n-alkanes at T = 298. 15 K
Figure. The vaporization enthalpies of the n-alkanes at T = K . The circles represent recommended vaporization enthalpies from the literature; the squares represent the vaporization enthalpies previously evaluated by correlation-gas chromatography;4 the triangles are the results of this study.

13. Figure. A plot of ln (p/po) versus 1/T for the n-alkanes; from top to bottom: : n-heneicosane; : docosane; : n-tricosane; : tetracosane; : pentacosane; : hexacosane; : heptacosane; : octacossane; : nonacosane; : triacontane; po is a reference pressure.

14. Figure. A plot of ln (p/po) versus 1/T for the n-alkanes from T = 298
Figure. A plot of ln (p/po) versus 1/T for the n-alkanes from T = K to T = 570 K (from top to bottom). , hentriacontane; , dotriacontane; , tritriacontane; , tetratriacontane; , pentatriacontane; , hexatriacontane; , heptatriacontane; , octatriacontane.

15. Since the values were all obtained by extrapolation, are they any good?

16. ln(p/po) = AT -3 + BT -2 + CT -1 + D
Compounds 10-8A B C D
heneicosane
docosane
tricosane
tetracosane
pentacosane
hexacosane
heptacosane
octacosane
nonacosane
triacontane

17. ln(p/po) = AT -3 + BT -2 + CT -1 + D
Compounds A 10-6B C D
hentriacontane
dotriacontane
tritriacontane
tetratriacontane
pentatriacontan
hexatriacontane
heptatriacontane
octatriacontane

18. Temp ln(p/po) ln(p/po)b ln(p/po)c K from ln(1/ta)a
A Comparison of the Vapor Pressure and Vaporization Enthalpy of Octacosane Obtained by Correlation Gas Chromatography with Literature Values.
Temp ln(p/po) ln(p/po)b ln(p/po)c
K from ln(1/ta)a d d d e e e e
lgHm( K)/kJ.mol-1
106.7a b d
athis work; bChirico, R. D.; Nguyen, A.; Steele, W. V.; Strube, M. M. J. Chem. Eng. Data 1989, 34, ;cMorgan, D. L.; Kobayashi, R. Fluid Phase Equil. 1994, 97, ; d“conformal” fit to the Wagner equation; eexperimental values.

19. T/K ln(p/po). ln(p/po)b ln(p/po)c. ln(p/po)d. ln(p/po)e. lgHm(T)a
T/K ln(p/po) ln(p/po)b ln(p/po)c ln(p/po)d ln(p/po)e lgHm(T)a lgHm(T)
from ln(1/ta)a
docosane c e d
tetracosane c e d
hexacosane e
octacosane b c e
athis work; bChirico, R. D.; Nguyen, A.; Steele, W. V.; Strube, M. M. J. Chem. Eng. Data 1989, 34, ;c “conformal” fit to the Wagner equation; Morgan, D. L.; Kobayashi, R. Fluid Phase Equil. 1994, 97, ; d Sasse, K.; Jose, J.; Merlin, J.-C., Fluid phase Equil. 1988, 42, ;eGrenier-Loustalot, M. F.; Potin-Gautier, M.; Grenier, P., Analytical Letters 1981, 14,

20. Tm/K lgH(Tm)a lgH(Tm)blgH(Tm) ln(p/po)a ln(p/po)b ln(p/po)
Table. Literature and Calculated Values of lgH(Tm) and ln(p/po) at T =Tm; Enthalpies in kJ.mol-1
Tm/K lgH(Tm)a lgH(Tm)blgH(Tm) ln(p/po)a ln(p/po)b ln(p/po)
Triacontane
Mazee
PERT212,c
Francis and Wood
PERT212,c
Piacente et al
PERT212,c
Hentriacontane
Mazee
PERT212,c
Piacente et al
PERT212,c
Dotriacontane
Piacente et al
PERT212,c
PERT212,c

21. Tm/K lgH(Tm)a lgH(Tm)blgH(Tm) ln(p/po)a ln(p/po)b ln(p/po)
Table. Literature and Calculated Values of lgH(Tm) and ln(p/po) at T =Tm; Enthalpies in kJ.mol-1
Tm/K lgH(Tm)a lgH(Tm)blgH(Tm) ln(p/po)a ln(p/po)b ln(p/po)
Tritriacontane
Piacente et al
PERT212,c
PERT212.c
Tetratriacontane
Mazee
PERT212,c
Francis and Wood
PERT212,c
Piacente et al
PERT212,c
Pentatriacontane
Mazee
PERT212,c
PERT212,c

22. Tm/K lgH(Tm)a lgH(Tm)blgH(Tm) ln(p/po)a ln(p/po)b ln(p/po)
Table. Literature and Calculated Values of lgH(Tm) and ln(p/po) at T =Tm; Enthalpies in kJ.mol-1
Tm/K lgH(Tm)a lgH(Tm)blgH(Tm) ln(p/po)a ln(p/po)b ln(p/po)
Hexatriacontane
Mazee
PERT212,c
Piacente et al
PERT212,c
Heptatriacontane
Piacente et al
PERT212,c
PERT212,c
Octatriacontane
Piacente et al
PERT212,c
PERT212,c
aLiterature value. bThis work. cCalculated using PERT2.

23. Any other uses for subcooled liquid vapor pressures and vaporization enthalpies?

24. lgHm tpceHm cTfus tpceHm crgHm
Table. Vaporization, Solid-Liquid Phase Change, and Sublimation Enthalpies at T = K.
lgHm tpceHm cTfus tpceHm crgHm
( K) Kc ( K)d ( K)e
heneicosane 2.5a 63.4  3.3
docosane 2.7a   3.5
tricosane 2.8a 75.5  4.9
tetracosane 2.8a 86.1  4.6
pentacosane 2.9a 84.4  4.3
hexacosane 3.2a 93.9  5.6
heptacosane 3.3a 89.5  7.9
octacosane 4.9a 100.3  6.4
nonacosane 5.1a 97.9  6.3
triacontane 5.3a   8.7 hentriacontane 1.2b
dotriacontane 1.4b 117.7  5.4
tritriacontane 1.4b 113.5  9.1
tetratriacontane 6b 127.4  9.0
pentatriacontane 178.19.2b   10.4
hexatriacontane 9.4b 128.8  13.7
heptatriacontane 187.69.6b
octatriacontane 9.8b

25. Many substances are released into the environment by a variety of natural and man promoted events. Combustion of fossil fuel for example leads to the production of a variety of polyaromatic hydrocarbons. Many of these material are large, non-volatile molecules and present in very small amounts. On account of their dispersal, they may be crystalline solids when pure but in the environment, they are present adsorbed onto particulates and their distribution in an west to east direction is governed by the prevailing winds. However, long-lived non-volatile materials tend to accumulate in the polar regions where their vapor pressure is the lowest. Their rate of dispersal in a northerly or southerly direction depends on their vapor pressure. It has been found that this is best approximated by the compounds sub-cooled vapor pressure.

26. Can the vapor pressure of the n-alkanes be used to evaluate vapor pressures of PAHs?
Retention Times for Some n-Alkanes and PAHs
T/K
t/min
CH2Cl
decane
dodecane naphthalene
biphenyl
tetradecane
pentadecane

27. Table 9. Equations for the Temperature Dependence of ln(1/ta) of Some n-Alkanes and PAHsa
Tm = K slnvHm/R intercept r2
naphthalene, biphenyl
decane  
naphthalene  
dodecane  
biphenyl  
tetradecane  
pentadecane  

28. slnvHm(413.2 K) lgHm (298.15 K) lgHm (298.15 K)
Table. Vaporization Enthalpies of Some PAHs in kJ.mol-1
slnvHm(413.2 K) lgHm ( K) lgHm ( K)
(lit) (calc)
decane 2.4
dodecane 2.8
naphthalene 2.5
biphenyl 2.9
tetradecane 3.3
pentadecane 3.5
lgHm ( K) = (1.4190.062) slngHm(Tm) – (2.420.93); r2 =

29. lgHm(298.15 K)(lit)a lgHm(298.15 K) Naphthalene
Summary 55.7 1.6b
biphenyl
Summary 65.5 2.9b
Sabbah, R.; Xu-wu, A. Chickos, J. S.; Planas Leitao, M. L.; Roux, M. V.; Torres, L. A. "Reference materials for calorimetry and differential scanning calorimetry," Thermochimica Acta 1999, 331, ; bthis work.

30. Naphthalene
Wagner Equation
ln(p/pc)=1/T/Tc [A(1-T/Tc)+B(1- T/Tc)1.5+C(1- T/Tc)2.5+D(1-T/Tc)5]
Tc/K pc/kPa A B C D
Biphenyl
Cox Equation
ln (p/po) = (1-Tb/T)exp(Ao +A1T +A2T 2)
Tb/K Ao A A2

31. Table. Correlation of ln(1/ta) with Experimental Vapor Pressures at 298.15 K.
ln(1/ta) ln(p/po)expt ln(p/po)calc
decane
naphthalene
dodecane
biphenyl
tetradecane
pentadecane
ln(p/po)calc = (1.2460.020) ln(1/ta)) – 1.0130.078; r2 =

32. ln(p/po)calca ln(p/po)lit C10H8 naphthalene -8.07 -7.98c, -7.91b
Table 14. A Comparison of Subcooled Liquid Vapor Pressures with Literature Values at T = K.
ln(p/po)calca ln(p/po)lit
C10H8 naphthalene c, -7.91b
C12H10 biphenyl d, -10.2b
aThis work. bLei, Y. D.; Chankalal, R.; Chan, A. Wania, F. “Supercooled liquid vapor pressures of the polycyclic aromatic hydrocarbons,” J. Chem. Eng. Data 2002, 47, 801 – 806; cChirico, R. D.; Knipmeyer, S. E.; Nguyen, A.; Steele, W. V. “The thermodynamic properties to the temperature 700 K of naphthalene and of 2,7-dimethylnaphthalene,” J. Chem. Thermodyn. 1993, 25, ; dChirico, R. D.; Knipmeyer, S. E.; Nguyen, A.; Steele, W. V.“The thermodynamic properties of biphenyl,” J. Chem. Thermodyn. 1989, 21,