## June 08, 2007

### Surface Tension

Surface Tension

In the literature surface tensions of liquids are usually given at one temperature only (often 15 or 20 °C). As the temperature is raised, the surface tension decreases and becomes zero at the critical point. Based on this observation the surface tension at temperature T2 can be estimated for most liquids from the following simple equation if surface tension at another temperature T1 and critical temperature Tc of the liquid are known

This equation has been proposed by Kharbanda (Kharbanda, O.P, Ind. Chemist, Vol. 31, April 1955, p. 187). The results are fairly accurate. Best results are obtained for nonpolar compounds. Experimental values of surface tension of some pure liquids at one temperature are given in the following table. Critical temperatures for many compounds can be found in Appendix A of Properties of Gases & Liquids by Reid, Prausnitz, and Poling.

Table: Experimental values of surface tensions of pure liquids (from Jasper, J.J., J. Phys. Chem. Ref. Data Vol. 1 (1972), p. 841)

Compound Temperature Surface tension
°C dynes/cm

Compound Temperature Surface tension
°C dynes/cm
Acetic acid 20 27.6
Acetone 25 24.0
Aniline 20 42.7
Benzene 20 28.9
Benzonitrile 20 39.4
Bromobenzene 20 35.8
n-Butane 20 12.5
Carbon disulfide 20 32.3
Carbon tetrachloride 15 27.7
Chlorobenzene 20 33.6
p-Cresol 40 34.9
Cyclohexane 20 25.2
Cyclopentane 20 22.6
Diethyl ether 15 17.6
Ethyl acetate 20 24.0
Ethyl benzoate 20 35.0
Ethyl mercaptan 15 23.9
Formamide 25 57.0
n-Heptane 20 20.1
Isobutyric acid 20 25.0
Methyl alcohol 20 22.6
Phenol 40 39.3
n-Propyl alcohol 20 23.7
n-Propyl benzene 20 30.0
Pyridine 20 37.2

Example:

Determine the surface tension of aniline at 80 °C. From above table the surface tension at 20°C is 42.7 dynes/cm, the critical temperature of aniline is 426 °C. Then the estimated surface tension at 80 °C from Kharbanda's correlation is 35.2 dynes/cm. Compared to the experimental value of 36.15 dynes/cm the error for the estimated value is 2.6%.

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