The vapour pressure of indane

J. Chem. Thermodynamics 1976, 8.601-602

Note The vapour

pressure of indane

D. AMBROSE and C. H. S. SPRAKJZ Division of Chemical Stat&r& Middlesex, TWll OL W, U.K.

National

Physical Laboratory,

Tecidington,

(Received IS December 1975)

In the course of proving the bubble-cap boiler (i) for the determination of vapour pressures by comparative ebulliometry we made measurements on a relatively highboiling substance, indane. The mole fraction of impurity in the sample was assessed by g.1.c. as 0.003. Temperatures T6s (treated as thermodynamic temperatures T) were measured by means of platinum resistance thermometers used with an automatic ax. bridge; these measurements were made before installation of automatic data-logging equipment, and the readings of the bridge were noted by an observer.(2) The measured vapour pressures (table 1) were fitted by the equations: log,,(p/kPa)

= 6.10462- 1574.16O/{(T/K)-67.079},

(1)

and WZologloWW

= 42 + s$l aAx),

(2)

where ao,. . ., a4 are adjustable coefficients, E,(x) is the Chebyshev polynomial in x of degree s, and x = {2T- (T,, + T,,,,)}/(T,,T,,,,) ;(‘) the numerical values are TABLE 1. Observedvapourpressures. Ap = (p,b.-p,& wherep,dOhasbeenobtainedfrom: 1, equation(1); II, equation(2)

I 355.006 361.162 366.632 371.183 375.110 382.344 389.541 393.495 396.706

4.343 5.650 7.069 8.471 9.860 12.920 16.722 19.150 21.330

II 4

0 2

2 -6

-3 -3

zf 14

1; 19

-4

91

401.747 407.868 412.664 419.678 425.629 432.119 437.913 444.603 449.671

25.174 30.586 35.453 43.667 51.799 61.998 72.392 86.085 97.757

12

II0

8’ -3

;

-12 6 -8

-;

zg

-;

1:;

I II 450.225 99.114 6 -6 450.681 100.222 -8 -18 458.077 119.861 18 16 463.319 135.493 13 22 470.337 158.841 -19 476.276 180.971 -26 1; 482.437 206.401 -8 47

602

NOTE

Tmin = 355 K, T,,, = 685 K, a, = 2712.942, CII = 1112.884, ~~ = - 11.067, (of = 5.916, a4 = -0.237. Equation (2) extends to the recently reported critical point (684.9 K, 3.95 MPa),(4) and from it a value 0.310 is obtained for the acentric factor w. Both equations give a normal boiling temperature Tb = 451.12 K with dp/dT = 2.49 kPa K-’ ; hence the enthalpy of vaporization AH, = 39.8 kJ mole1 and the entropy of vaporization AH,/T = 88.3 J mol-r K-‘. For the calculation of AH,, the second virial coefficient B was estimated@) as - 1450 cm3 mol-’ and the molar volume V, of the liquid was taken as 150 cm3 mol-l (an error of 100 cm3 in the estimated value of (B- Vr) gives rise to an error of 0.1 kJ mol- ’ in AH,). At 298.15 K equation (2), use of which is preferable for extrapolation, gives a vapour pressure p = (0.204 + 0.004) kPa, with dp/dT = (0.0135f0.0005) kPa K-r and hence AH, = (49f 1.5) kJ mol-r where the uncertainties quoted are estimated ranges of the probable errors arising from the extrapolation. Stull et aI.@) reported values for the vapour pressure from 6.5 to 104 kPa that are about 0.2 per cent higher than those calculated from equations (1) and (2) and correspond to a normal boiling temperature Tb = 451.0 K. We acknowledge assistance by Miss R. F. Anthony in making the observations. REFERENCES 1. Ambrose, D. J. Phys. E 1968, 1,41. 2. Ambrose, D.; Sprake, C. H. S. J. Chem. llermodynamics 1970,2, 631. 3. Ambrose, D.; Counsell, J. F.; Davenport, A. J. J. Gem. Thermodynumics 1970,2, 283. 4. Ambrose, D.; Broderick, B. E.; Townsend, R. J. Appl. Chem. Biotechnol. 1974,24, 359. 5. Pitzer, K. S.; Curl, R. F. J. Amer. Chem. Sot. 1957, 79, 2369. 6. Stull, D. R.; Sinke, G. C.; McDonald, R. A.; Hatton, W. E.; Hildenbrand, D. L. Pure Appl. Chem. 1%1,2, 315.