# What is the relationship between temperature and viscosity of liquids and gases?

Printer-friendly version
Title:
What is the relationship between temperature and viscosity of liquids and gases?
Topic:
Viscosity
Question:

What is the relationship between temperature and viscosity of liquids and gases?

Answer:

SEED Expert Bernd Eggen answers:
There is an exponential (or logarithmic) dependency between viscosity n and temperature T, recall the formula:

where A and dEvis are constants specific for each liquid and R is the universal gas constant.

Also note, there is a conversion formula v = n/p with v being the kinematic viscosity and n the dynamic viscosity.

So plotting log(n) against 1/T (in Kelvin) gives a straight line, therefore the higher the temperature T, the smaller is 1/T and the lower is viscosity n of the liquid.

Also recall Hildebrand's formula, that viscosity is related to the ratio between free volume and occupied volume (Vo):

where B is another constant and V is the actual volume.
Note that in latter formula, the temperature is implicitly represented in the volume V as most liquids expand when heated.