1990
INDUSTRIAL AND ENGINEERING CHEMISTRY
per cent of conversion. On slow cooling strontium carbonate was observed to crystallize first from the clear solutiolis proving it to be the least soluble arrangement of the ions. -4plot of the data in columns 1 through 6 and column 9 of Table IV fell along a straight line. Treatment of these data by the method of least squares yielded the equation:
Y
= -3.57
Vol. 40, No. 10
ACKNOWLEDGMENT
The authors wish to acknowledge the advice and suggestions of Thomas B. Crumpler in the development of the prohlrm and in the preparation of this paper. LITER&TUKE CITED
+ 98.3X
where X equals the moles of sodium carbonate per mole of strontium sulfate and Y equals the per cent conversion of strontium sulfate to the carbonate. From this it was shown that there must be a t least 0.0363 mole of sodium carbonate present per mole of strontium sulfate before any of the strontium sulfate is converted to the carbonate. In the same way it was found that a t least 1.053 moles of sodium carbonate per mole of strontium sulfate must be present before all of the strontium sulfate is converted t o the carbonate.
(1) Booth, €1.S.,U. S.Patent 2,013,401 (Sept. 3 , 1945) (2) I b i d . , 2,048,593 (July 21, 1936). (3) Ibid., 2,112,903 ( h p ~ i 5l , 1938). (4) 1 b X 9 2,112,904. ( 5 ) Newman, E. W., J . Am. Chem. Soc., 56, 879 84 (1933). (6) Townley, R. TT., Ibid., 59, 631-33 (1937), (7) Voail'ev, A . M ~Trans. ? Kirot, Inst. Chem. Technol. Kazon., 3$ 37
(1935)
~
RECEIISD December 9, 1946. Based on X S . thesis submitted by a.M. Buaey t o Graduate Chemistry Faculty of Tulane University, ,Illne 1941.
so ENTHALPY, ENTROPY, AND SPECIFIC HEAT F
T h e enthalpy of liquid isopropyl alcohol referred to 0' C. has been determined up to 200' C. by use of a furnace and ice calorimeter. Derived values of specific heat and entropy are also given.
T
HIS report describes measurements which extend the thermal data on liquid isopropyl alcohol into a previously unexplored region; no measurements of specific heat have been reported heretofore above 54" C. The detelmination of enthalpy was accomplished by heating t,he sample enclosed in a capsule to a desired temperature in a furnace, dropping it into an ice calorimeter, and measuring the heat evolved in cooling t,he sample and capsule to 0' C. After the enthalpy was determined a t several temperatures, the specific heat was obtained by differentiation of the enthalpy-temperature funct,ion. EXPERIiMENTAL
O
c.
and 0.860 giam in the low filling experiments a t 155.0" &ndt 200.7" C. Three shields were used above the capsule instead oi the two that m r e used in other measurements ( 1 , s ) . The high filling sciics >vas begun with three experiment&st 200 7" C which gave 933.8,931.5, and 930.8 calories of heat transieii cd t o the calorimeter, respwtivrly. These were followed by rvperiments a t the three lower temperatures which appeared t o show a random scattering of results and then by three more experiments a t 200.7' C. which gave 931.3,929.1, and927.9 calories, respectively. The d o w i m r d tiend in the results a t 200.7" C , over a range of 0.67, n as taken as indicating chemical change of the sample during the time spent in the furnace a t that temperreture. This time was about 1 hour per experiment. With soma arbitrariness, the value of the heat which would ha,ve been transferred in an experiment at 200 7" before any chemical rcactiort had occurred v a s talrcn to be 933 7 calories and the results for the experiments a t the lower temperatures were increased b j
A commercial sample of 99% isopropyl alcohol vas refluxed for 12 hours over freshly calcined calcium oxide. The entire batch distilled a t 82.2" C. (760 mm.), the sample being taken from the middle half. The sample was sealed in a Monel capsule of IO-ml. capacity. S o attempt was made to expel air from the capsule and sample before sealing.
I t is calculated that the error resulting froni the presence of air did not exceed 0.1%. The authors believe that errors resulting from all impurities in the original sample are small in comparison n ith other errors which are mentioned below. The apparatus and experimental technique have been described recently ( 1 , 4 , 4 ) . In the present measurements, experiments were made with a high filling of sample in the capsule (HF) and with a low filling of sample (LF) at four temperatures between 55.0' and 200.7" C. The differences between the two series of results gave the enthalpy of the saturated liquid-Le., liquid which is in equilibrium with its own vapor-after application of a correction described later. The amount of sample was 4.045 grams in the high filling series, 0.538 gram in the low filling experiments a t 55.0" and 110.4' C.,
TEMPERATURE ldea CJ
Figure 1.
Specific Heat of Liquid Isopropyl Alrohol
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1948
1991
1:
OF SATURATED LIQUIDISOPROPYL ALCOHOL This technique is described in (I)]. The calculation of Hsatd TABLE I. ENTHALPY is summarized in Table I. (1 oal. = 4.1833 int. joules)
0 208.0 489.5 686.9 933.7
6)
66.0 110.4 165.0 '200.7
0 87.7 186.6 316.4 436.4
1.247 1.325 1.425 1.548 1.789
0.0117 0.301 2.76 10.0 27.7
0.0 0.1
0.00073 0.0145 0.0910 0.254 0.562
0 34.5 79.0 120.4 167.7
1.2 4.1 11.5
SPECIFICHEAT,AND ENTROPY OF TABLE 11. ENTHALPY, SATURATED LIQUIDISOPROPYL ALCOHOL (1 oal. = 4.1833 int. joules)
t,
Csatd,
Hsatd]:,
c.
Ca1.G. - 1 0 11.3 (14.4) 24.0 38.1 53.6 70.1 87.6 106,O 125.4 145.7 167.0
0 20
"E'
BO 80 100 I20 140 160 180
200
CaLG.-lDeg.-'C. 0.541 0.596 (0.613) 0.670 0.742 0 798 0.848 0.894 0.939 0.983 1.024 1.062
Ssetd]
\,
Ca1.G. -1Deg. -1K. 0 0.0400 (0.0503) 0.0817 0.1255 0.1714 0.2157 0.2612 0.3067 0,3521 0.3974 0,4424
0.28% to account for the change that had already occurred by the time they were observed. This difficulty was avoided in the low filling series by taking a fresh sample and progressing from the lowest temperature to the highest. The experiments at 200.7" again showed a small downward trend, but the experiments at the lower temperatures required no correction, as there was no evidence of reaction at the time they were made. RESULTS
According to Osborne ( 7 )
where Q
I" I' 0
m Hastd
0
T
= heat evolved in cooling capsule
and sample from t o to 0" C.
= mass of sample = enthalpy per gram
of saturated liquid
referred to 0 C.
v
= absolute temperature = specific volume of saturated liquid
P
= vapor pressure
11" -
rapidly with temperature, amount& to 7% of Hsstd
.
Be-
cause of the long extrapolations involved, an error of 1% in
]I"
was obtained using Simpson's rule. Values of enthalpy, entropy, and specific heat resulting from this treatment are given in Table 11. Error resulting from linear interpolation between adjacent table values will not exceed experimental error. The values of specific heat are shown graphically in Figure 1 together with the C p data of Kelley ( 5 ) , Williams and Daniels (9), and Zhdanov (IO). The values of Williams and Daniels are 674 higher than those of this investigation, which may indicate contamination of their sample'by water. I t will be noted that a gentle hump occurs in the specific hrat curve in the neighborhood of 70" C. The data from the present investigation by itself are not sufficiently specific below 55' C. to establish a hump which results entirely from the adjustment to fit Kelley's data just mentioned. The question of the reality of the hump is therefore connected with the accuracy of Kelley's data as well as with the accuracy of the data from this investigation. The experimcnts on isopropyl alcohol were performed nearly a year before those described in ( I ) and a t a time when the best technique for operation of the ice calorimeter had not yet been evolved. In eighteen experiments in both series, excluding the high filling experiments a t 200.7", the average deviation of
Q
I n order to evaluate the last term in Equation 1it was necessary to extrapolate the available vapor pressure data for isopropyl alcohol (4, 6 ) above 90' C. A method involving comparison with the vapor pressure of water was employed. To obtain the specific volume, v, available measured densities near room temperature were added to calculated densities of saturated vapor and the sums were extrapolated (law of rectilinear diameter), making some allowance for curvature of the function. Saturated vapor densities were calculated from an equation of Meyers (6) using critical data from (4).The term, TvdPIdT, increases
Haatd
The specific heat of saturated isopropyl alcohol was obtained using the relation Csatd = dHs,td/dT - vdP/dT (2) The method used in determining dH,,,d/dT and in obtaining smoothed values of enthalpy is given in ( 1 ) . The term, IjdPldT, amounted to 2.3%of CBB.td at 200 O C., decreasingrapidly to 0.15% at the boiling point, below which it is negligible. Since the specific heat as determined by the present method is somewhat indeterminate below 55 O , the C, data of Kelley (5)extending from low temperatures up to 20' C. were used to establish the form of the saturation specific heat function in the range 0" to 55". (The difference between C, and CBstd is negligible a t temperatures below the boiling point, being 0.17, or less.) The values of specific heat from 0' t o 20' were chosen SO as to coincide with a smooth curve through Kelley's data; the values from 20" t o 55' were adjusted so as to provide a smooth specific heat curve while giving correct values of the enthalpy a t and above 55" by integration. The saturation entropy referred to 0 O C.
is easily possible from this SOL~CFL. [The dependence of
the accuracy of the enthalpy values upon extrapolated values of v and dP/dT could have been reduced, provided the enthalpy of the empty capsule had been known from separate experiments.
1:
from the mean was 0.08% or 0.3 calorie, which is three timee
the corresponding quantity reported in the later work (1). The largest sources of error in this investigation, given in the order of their magnitudes, wcre the TvdPldT correction term and the apparent chemical reaction of the sample during the measurements. The results (enthalpies, entropies, and specific heats) are estimated to be accurate to about 1% except below K4° C., where they may be less accurate. LITERATURE CITED
(I) Corruccini, R. J., and Ginnings, D. C., J . Am. Chem.
BOC.,
69,
2291 (1947).
(2) Ginnings, D. C., and Corruccini, R. J., J . Research Natl. Bur Standards, 38,583 (1947). (3) Ibid., 38, 593 (1947). (4) International Critical Tables, Vol. 3, p. 248, New York, McGraw-Hill Book Co., 1928. (5) Kelley, K. K., J . Am. Chem. Soc., 51, 1146 (1929). (6) Megers, C. H., Bur. Standards J. Research, 11, 691 (1933). (7) Osborne, N. S., Ibid., 4,609 (1930). (8) Parks, G. S., and Barton, B., J,Am. Chern. SOC.,50,24 (1928). (9) Williams, J. W., and Daniels, F., Ibid., 46, 903 (1924). (10) Zhdanov, A. K., J . Gen. Chem. (U.S.S.R.), 15,895 (1945).
RECEIVED June 11, 1947.
