Properties of Liquids Surface Tension and Viscosity

You have seen that molecules tend to escape the liquid state and form a vapor. The vapor pressure is the equilibrium partial pressure of this vapor over the liquid it increases with temperature. The boiling point is the temperature at which the vapor pressure equals the pressure applied to the liquid. Both vapor pressure and boiling point are important properties of a liquid. Values of the vapor pressure for some liquids at 20°C are listed in Table 11.2 (column 3). Two additional properties given in Table 11.2 are surface tension and viscosity. All of these properties, as you will see in the next section, depend on intermolecular forces, which are related to molecular structure. 

Substance Molecular Weight (amu) Vapor Pressure (mmHg) Surface Tension (J/m ) Viscosity (kg/m s) 

The water bug seems to skate on the surface skin of the water, which is actually a result of surface tension. 

Energy is needed to reverse the tendency toward reduction of surface area in liquids. Surface tension is the energy required to increase the surface area of a liquid by a unit amount. Column 4 in Table 11.2 lists values of the surface tension of some liquids at 20°C. 

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We see that two important properties of liquids—surface tension and viscosity— can be understood in terms of intermolecular forces. (11.3)... 

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