Effect of Temperature on Viscosity

Effect of Temperature on Viscosity

Effect of Temperature on Viscosity

What is the Effect of Temperature on Viscosity ?

The viscosity of a liquid is generally decreases with rise in temperature. This decrease is about 2% per degree rise of temperature in many cases. This has been explained in terms of Hole Theory of liquids.
The variation of viscosity (η) with temperature can be expressed by the following relationship-
η = AeEa/RT -----[Equation-1]
where A is constant and Ea is called the activation energy for viscous flow.
Taking natural log on both sides, we get-
ln η = A + Ea/RT
or ln η = ln A + Ea/R + 1/T -----[Equation-2]
A plot of ln η versus 1/T should be a straight line
Effect of Temperature on Viscosity Graph
The gas viscosity (η) will increase with temperature. According to the kinetic theory of gases, viscosity should be proportional to the square root of the absolute temperature, in practice, it increases more rapidly.

Effect of Pressure on Viscosity