24. Surface Tension

yaboiemil's version from 2016-02-04 21:11


1. Surface tension is the work required to overcome to cohesive forces in a liquid during the increasing of the liquid
surface by molecules arising from within its volume.
2. It occurs because molecules as the phase interface do not have like molecules on all sides of them - they
therefore adhere more strongly to those associated with them on the surface of the liquid forming a "film".
3. The force required to overcome to cohesive forces of the liquid.
4. Surface tension forces the liquid to become as small as possible (e.g. spherical balls)

Surface Tension Equation:



Question Answer
SigmaSurface Tension
FForce acting in parallel w/ surface of liquid, perpendicular to length unit
lLength Unit
EEnergy released when A is reduced to zero
ASurface Area


5. Different substances have different Surface Tension.
6. Higher Surface tension results in higher internal pressure, summarized by the...

Laplace Equation:



Question Answer
∆pDiff. in pressure between inside and outside
sigmaSurface tension
rRadius of Curvature of Liquid


7. At the point that a gas and liquid phase both make contact with a solid surface (Glass),
the behavior of the liquid will depend on the ratio of cohesion/adhesion forces
8. If adhesion>cohesion, the glass will be wet and capillary elevation occurs
9. If adhesion< cohesion, the glass will not be wet, and capillary depression occurs
10. A small amount of ions that are dissociated into the liquid will increase cohesive forces
and therefore surface tension. Usually, decreases it though. Described by...

Gibb's Absorption Equation:



Question Answer
GammaSurface concentration of substance
cconcentration of substance
RUniversal Gas Constant
TAbsolute Temperature
∆sigmaChange in surface tension
∆cChange in surface concentration of surfactant


11. Surfactants are Surface Active Agents. They amphiphilic (hydrophilic and phobic parts).
12. They have v. specific jobs in the body such as helping Alveoli:
13. Alveoli are prevented from collapse during the expiration phase by phospholipid surfactants
on the alveolar membrane which lowers surface tension. It is at its greatest concentration when
the alveoli is at its smallest (expiration phase), ensuring maximum effect.
14. Bile acids help in digestion of fats.
15. Surface tension is measured using a tensiometer and stalagometer.