The document summarizes Eyring's molecular theory of viscosity of liquids. According to the theory, molecules in a liquid are constantly moving within a "cage" formed by neighboring molecules. Occasionally, a molecule will gain enough energy to escape its cage and jump into an adjacent empty space. The viscosity of a liquid depends on the rate at which these jumps occur and the distance traveled during each jump. The document provides example problems calculating the viscosity of benzene and water at different temperatures based on this theory.

1. 18CHE14-TRANSPORT PHENOMENA
Theory of viscosity of liquids
Manju Sri A
Assistant Professor
Department of Chemical Engineering

2. Molecular theory of viscosity of liquids
• Kinetic theory (monoatomic liq)-Kirkwood and
coworkers-not easy to use
• Eyring and coworkers-less well grounded-but gives a
qualitative picture on momentum transport-permits
rough estimation of viscosity.
• According to Eyring’s theory: Pure liquid at rest –
molecules are constantly in motion within its cage
formed by nearest neighbours.
• Cage is represented as the energy barrier of height
• Molar free energy of activation-
• Liquid at rest continuously undergoes rearrangements
molecules at times escape from its cage to its adjoining
hole in each of the coordinate directions of length “a”
and frequency “γ”

4. • Distance travelled for each jump – “a” at a
frequency of
• Forward jump (+) and Backward jump (-)
• The net velocity is “a” times the the net
frequency

8. Problems
10.Estimate the viscosity of liq.benzene at 293.2
K
11. Estimate the viscosity of saturated liq.water
at 0 and 100 deg.celsius.
Data: molar volume=18cm3/gmol.

9. Solution for problem 10