Heats, equilibrium constants, and free energies of...
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U. S. Department of Commerce National Bureau of Standards Research Paper RP1976 Volume 42, April 1949 Part of the Journal of Resea rch of the National Bureau of Standards Heats, Equilibrium Constants, and Free Energies of Formation of Cyclopentene and Cyclohexene 1 By Morton a. Epstein,2 Kenneth S. Pitzer,3 and Frederick D. Rossini 4 For cyclopentene and cyclohexene, values are pres ented for the following thermody- namic prop erti es to 1,500° K: heat-content fun ct ion, free-energy function, e ntr opy, h eat cont ent, heat capaci ty, heat of format io n from the elements, free energy of forma ti on from t he elements , and logarit hm of the equilibrium con st ant of formation from the element s. Equilibrium constan ts ar e given in graphical form for some reactions of isomerization, dehydrogenation, and disproportionation. As part of th e work of the American Petroleum Ins titu te R ese ar ch Project 44 at the Na tional Bureau . of Standards and th e University of California, valu es hav e b een compiled for the thermodynamic properti es in the gaseous s tat e to 1,500° K of the heat-cont ent function, free- energy function, entropy , heat cont ent, heat capacity, heat of formation, fr ee energy of forma- tion, and lo garithm of the equilibrium constant of formation for cyclopen tene and cyclohexen e. Calculations have also b een mad e of th e free energies and equilibrium cons tants of a numb er of reactions involving isomerization, de hydro- genation , and disproportionation of these com- pounds. The valu es of the cons tant s u se d in th e present calculat ions ar e as follows [1,2] 5: The calorie is th e conventional thermochemical calorie defined as 4.1840 absolute joules; the absolute temper- atur e of the ice point is 273.16 ± 0.010° K; th e gas cons tant is 1.98719 ± 0.0001 3 cal/deg mole. For cyclop e nt en e and cyclohex en e, the valu es 1 This in vestigation was performed as a part of the work of tbe Ameri can Petroleum I nstitute Research Project 44 at the Natioual Bureau of Stand ar ds and tbe University of California. 2 Research Associate on t he Amer ican P e!ro!eum Institute Research Project 44 at the Nat ional Bureau of Standards. 3 Associate Director of the American Petroleum Institute ResealCh P roject 44 at tbe Uni vers ity of California. Berkeley, Cal. • D irector of the American Petroleum Institute Research P roject 44 at· the Nat ional Bureau of Stand ards. , Figu res in brackets indicate the literat ure references at the end of tbis paper. Heats, Equilibrium Constants, and Free Energies of the heat- content function, fr ee-en ergy fWl ction, and heat capacity were taken from referenc e [3]. As usual, th e value of the entropy is given by the value of the heat- cont ent function less the value of the fr ee -energy function, and th e heat cont ent is obtained by multiplying th e value of the heat - cont ent function by the temp eratur e. The r esulting values of th e th ermodynami c functions ar e given in table 1, which includ es values of the following properties from 0° to 1,50,0° K : heat-content function, free-energy function, entropy , heat content , and heat capacity. Valu es of th e s tandard heat of formation at 25 ° C of gaseous cyclopent en e and cyclohexene, from carbon (s olid, graphit e) and hydrog en (g aseous), were calculated from th e valu es for th e standard heat of formation for the liquid s tat e cal- culat ed by Prosen, Yenchius, and Rossini [4] from experime ntal values for th e heats of combustion, together with values for th e s tandard heat of vaporization calcul at ed by Wagman and Rossini [6 ] from vapor pr essur e data of Forziati and Ros- sini [7]. Th e valu es for th e s tandard heat of forma- tion from th e elements, at 25° C, !1HjO, from refer- ence [4] ar e as follows: Cyclopent ene (liquid), 1.16 ± 0.16 kcal/mole; cyclohexene (liquid), - 9 .7 0 ± 0.19 kcal/mol e. Th e valu es for the stand ard heat of vaporization at 25° C, !1H vo, from reference [6], ar e as foll ows: cyclopenten e, 6.71 ± 0.07 kcal/mole; cyclohexene, 8.00 ± 0.08 kcal/mole. 379
Transcript of Heats, equilibrium constants, and free energies of...
U. S. Department of Commerce
National Bureau of Standards
Research Paper RP1976
Volume 42, April 1949
Part of the Journal of Research of the National Bureau of Standards
Heats, Equilibrium Constants, and Free Energies of Formation of Cyclopentene and Cyclohexene1
By Morton a. Epstein,2 Kenneth S. Pitzer,3 and Frederick D. Rossini 4
For cyclopentene and cyclohexene, values are presented for the following thermody
namic properties to 1,500° K : heat-content fun ction, free-energy function , entropy, heat
content, heat capacity, heat of format ion from t he elements, free energy of formation from
t he elements, and logarithm of t he equilibrium constant of formation from the elements.
Equilibrium constan ts are given in graphical form for some reactions of isomerizat ion,
dehydrogenat ion, and disproportionat ion.
As part of the work of the American P etroleum Institute R esearch Proj ect 44 at the National Bureau . of Standards and the University of California, values have been compiled for the thermodynamic properties in the gaseous state to 1,500° K of the heat-content function, freeenergy function, entropy, heat content, heat capacity, heat of formation, free energy of formation, and logarithm of the equilibrium constant of formation for cyclopentene and cyclohexene. Calculations have also been made of the free energies and equilibrium constants of a number of reactions involving isomerization, dehydrogenation, and disproportionation of these compounds.
The values of the constants used in the present calculations are as follows [1,2] 5: The calorie is the conventional thermochemical calorie defined as 4.1840 absolute joules ; the absolute temperature of the ice point is 273.16 ± 0.010° K; the gas constant is 1.98719 ± 0.00013 cal/deg mole.
For cyclopentene and cyclohexene, the values
1 This in vestigation was performed as a part of the work of tbe American P etroleum I nstitu te Research P roject 44 at the Natioual Bureau of Standards and tbe University of California.
2 Research Associate on the Amer ican Pe!ro!eum Institute Research Project 44 at the National Bureau of Standards.
3 Associate Director of the American Petroleum Institu te ResealCh P roject 44 at tbe University of California. Berkeley, Cal.
• D irector of the American Petroleum Inst itute Research P roject 44 at· the National Bureau of Standards.
, Figu res in brackets ind icate the literature references at the end of tbis paper.
Heats, Equilibrium Constants, and Free Energies
of the heat-content function, free-energy fWlction, and heat capacity were taken from reference [3]. As usual , the value of the entropy is given by the value of the heat-content function less the value of the free-energy function, and the heat content is obtained by multiplying the value of the heatcontent function by the temperature.
The resulting values of the thermodynamic functions are given in table 1, which includes values of the following properties from 0 ° to 1,50,0° K : heat-content function, free-energy function, entropy, heat content, and heat capacity .
Values of the standard heat of forma tion at 25° C of gaseous cyclopentene and cyclohexene, from carbon (solid, graphite) and hydrogen (gaseous), were calculated from the values for the standard heat of formation for the liquid state calculated by Prosen , Yenchius, and Rossini [4] from experimental values for the heats of combus tion, together with values for the standard heat of vaporization calculated by Wagman and Rossini [6] from vapor pressure data of Forziati and Rossini [7]. The values for the standard heat of formation from the elements, at 25° C, !1HjO, from reference [4] are as follows: Cyclopentene (liquid), 1.16 ± 0.16 kcal/mole ; cyclohexene (liquid), - 9.70 ± 0.19 kcal/mole. The values for the standard heat of vaporization at 25° C, !1Hvo, from reference [6], are as follows: cyclopentene, 6.71 ± 0.07 kcal/mole; cyclohexene, 8.00 ± 0.08 kcal/mole.
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(..) co o
...... o ~ ::s a o -~ (1) III (1)
a n p-
I
TABLE 1.-Values of the thermodynamic functions, for the ideal gas state, to 1,500° K , for cyclopentene and cyclohexene
rr c mperature if) oK
Compound (gas) For· 0 I 200 I 298.16 I 300 I 400 I 500 I GOO I 700 I 800 I 900 I 1,000 I 1,100 I 1,200 I 1,300 I 1,400 I 1,500 mula I
Ueat·contcnt fUDction , (flo- lfa) / T, in cal/deg mole -.-
~ I Cyc1opentene _________ C,U , 9
971
1161 I 11. 65 [ 14. 12 1 16. 98 1 19.90 I 22. 71 I 25.3" I 27. 82 1 30.00 I 32 19 I 34 13 1 35. 92 1 37. 57 1
39.10 Cyclohexene __________ C,B " 10 75 13.98 14.05 18.04 22.20 26.20 29.93 33.35 36. 47 39.33 41. 94 44 .34 46.53 . 48.55 50.42
I Free-energy fnnction, (FO-E~) /T, in cal/deg mole
. I Cyclopentene __ _____ __ C,U, 0 1-
03371
-57. 62 1 -57. 69 1 -61.37 1 -64. 82 1 -68. 18 1 -71.46 1 -74. 67 1 -77.80 I --80. 85 1 -83. 81 -86. 70 I -89.50 I -92. 23 1 -94.87 Cyclohexene ___ ___ ____ C,R " o -55. 43 -60.29 - 60.38 -64.96 -69. 43. - 73.84 - 78. 16 -82.38 -86. 49 -90.48 -94.36 -98. 12 -101. 75 - 105.27 -108.68
I
Entropy, So, in cai/dcg mole
Cyc1opcntcnc _____ ____ C,U, ~ I 63. 43 1 69 23 1 69. 34 1 75. 49 1 81.80 I 88081
94 171 ]00. 03 1 105. 62 1 110. 94 1 116.00 1 120. 83 1 125. 42 1 129.80 I 133.97 Cyclohexene ______ ____ C~Hlo G6.18 74.27 74.43 83.00 91.63 100.04 lO8. 09 115.73 122.96 129.81 136.30 142.46 148.28 153.82 159.10
Ueat content, (HO-H~), in cal/mole
Cyclopentene ___ ______ C,ll, ~ I 1,994 3, 462
1 3, 49s 1 5, 648 1 8, 490 11,940 I 15,900 20,290 25,040 30, 090 35,410 40,960 46,700 ;2,600 58,650
Cyclohexene _________ _ C,U " 2, 150 4,168 4,215 7,216 11 , 100 15,720 20,950 26,680 32,820 39,330 46, 130 53,210 60,490 67,970 75,630 ,
I Ueat capacity, C;, in cal/dog mole
Cyclopentene ___ ______ C,U, ~ I 12.33 1 l7.9s l 18.08
25. 08 1 31. G2 1 37 19
1
41. 86 1 4S 781 49. II 51. 94 54. 37 1
·5G.45 58.24 59.79 61. 13 Cyclohexene __________ C,U" 16.32 25. JO 25.28 34.64 42.78 49.45 54.92 59.49 63.34 66.62 69.43 71.85 73.92 75.72 77.27
Heat of formation, ilHfo, in kent/mole
Cyelopentenc _________ C,H, 7.05 3. 14 I. 16 I. 12 - 0. 74 1
-2.28 -3.51 '--4. 49 -S.22 I -5. 75 1 -6. 09 1 -G. 29 I -6.35 -6.35 -G. 27 -6. 15 Cyclophexcne __ _____ __ C,R , -2.24 -7.44 -9.70 -9.74 -11.69 - 13.21 - 14.35 - 15. 18 - 15.74 -16.07 -16. 19 -16. 14 -15.95 -15.70 - 15. 36 - 14.96
Free energy of formation, AFfo in kcal/molc --
Cyclopentenc _________ C,H, 7.05 -------- 19.77 19.89 26.43 33.41 40 681
48.11 55.68 63.31 I 71. 01 78.73 86.46 94.20 101. 9 109.6 Cyclohexene __________ C,U " -2.24 -------- 17.12 17.28 26. 60 36.36 46.38 56.58 66. $6 77. 22 S7.60 97. 96 lOS. 3 liS. 7 129.0 139.3
Logarithm of equilibrium constant of formation, log" KJ
Cyclopcntene _________ C,H, -I' ·····1 -" .. ' 1 -"""' 1 -'" 'w 1 -" "" 1 -'''''' 1 -""" 1 - ". "" 1 -""" 1 -'" ' " 1 -"'·' 1 -'" '" I -"~' - 15.900 1 - 15.975 Cyclohexenc __________ CoR IO 00 _____ __ _ -12.548 - 12.592 - 14.533 - ]5.S92 - 16.895 - 17.664 - 18.266 - 18.750 - 19. 143 - 19. 462 - 19.727 - 19.951 -20. 136 -20.294
The method of calculating values of the standard heat of formation, the standard free energy of formation, and the logarithm of the equilibrium constant of formation for the different temperatures in the range 0° to 1,500° K is the same as that described in section IV, 1 of reference [5] .
The resulting values for the formation of the given hydrocarbon in the gaseous state, from the elements carbon (solid, graphite) and hydrogen (gaseous), each in its thermodynamic standard reference state, are included in table 1, which gives values of the following properties to 1,500° K: heat of formation, free energy of formation, and logarithm of the equilibrium constant of formation.
6
4
2
o
-4
-6 --.CYCLOPENTANE . CYCLOPENTENE+H,
-B
TEMPERATURE IN 'K
F IGURE 1. Dehydrogenation of cycloparaffins to cycloolefins.
T he curves give the logarithm of the equilibrium constant as a function of temperature for the following reactions in the gaseous state:
C,R lO (gas, cyclopentane)=C,R , (gas, cyclopentene)+R , (gas) .
C,R " (gas, cyclohexane)=C,R IO (gas, ryclohexene)+R , (gas).
Heats, Equilibrium Constants, and Free Energies
In figure 1 are plotted, as a function of temperature, values of the logarithm of the equilibrium constant for the reactions of dehydrogenation of cydopentane to cyclopentenc and of cyclohexane to cyclohexene.
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6
4
o .......-- 3 CYCLOHEXENE.BENZENE+
2 CYCLOHEXANE
-4
-6
-B --CYCLOHEXENE , BENZENE +2Hz
-10
TEMPERATURE IN 'K
FIGURE 2_ Dehydrogenation of cyclohexene to benzene and dis proportionat-ion of cyclohexene to benzene and cyclohexane.
The curves give tbe logarithm of tbo equilibrium constant as a function of temperature for tbe following reactions in the gaseous state:
C,R IO (gas, cyclohexene)=C,R , (gas, benzene)+2R , (gas).
3C,R IO (gas, cyclohexene)=C,R , (gas, bcnzene)+2C,R " (gas, cyclohoxano) .
In figure 2 are plotted, as a function of temperature, values of the logarithm of the equilibrium constant for the dehydrogenation of cyclohexene to benzene and for the disproportionation of cyclohexene to cyclohexane and benzene.
In figure 3 are plotted, as a function of temperature, values of the logarithm of the equilibrium
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0
-5
-10 :.c
0
0> 52
-15
-20
-25
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TEMPERATURE IN ·C
327 527 927 1127
A: CYCLOPENTENE . I-trons-3' PENTADIENE
B: CYCLOPENTENE. 1- PENTYNE
C: CYCLOHEXENE.I - HEXYNE
TEMPERATURE IN "K
FIGURE 3. I somerization of cycloolefins to diolefins and to acetylenes.
The curves give the logarithm of the equilibrium constant as a function of temperature for the following reactions in the gaseous state :
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(A) C,R, (gas, cyclopentene) =C,R , (gas, 1·trans·3-pentadiene).
(E) C,R , (gas, cyclopentene) =C,R , (gas, l-pentyne) .
(C) C,RIO (gas, cyclohexene) =C,R IO (gas, l-hexyne).
constan t for the isomerization ofcyclopentene to 1-pentyne, of cyclopentene to I-trans-3-p en tadiene, and of cyclohexene to 1-hexyne.
References
[1] Selected values of chemical thermodynamic properties (December 31, 1947). National Bureau of Standards.
[2] Selected values of properties of hydrocarbons. Table u. (December 31, 1947). American Petroleum Institute Research Project 44, Natio'nal Bureau of Standards.
[3] C. W. Beckett, N. K. Freeman, and K.S. Pitzer, J . Am. Chern. Soc. 70,4227 (1948).
[4] E. J . Prosen, F. Yenchius, and F. D . Rossini, National Bureau of Standards. Unpublished.
[5] D . D . Wagman, J. E. Kilpatrick, W. J . Taylor, K. S. Pitzer, and F. D . Rossini, J. Research NBS 34, 143 (1945) RP1634.
[6] D. D . Wagman and F. D. Rossini, National Bureau of Standards. Unpublished.
17] A. F . Forziati and F . D. Rossini, National Bureau of Standards. Unpublished.
WASHINGTON , January 11 , 1949.
Journal of Research
