How does Temperature Change Viscosity in Liquids and Gases?

With an increase in temperature, there is typically an increase in the molecular interchange as molecules move faster in higher temperatures.

The gas viscosity 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.

In a liquid there will be molecular interchange similar to those developed in a gas, but there are additional substantial attractive, cohesive forces between the molecules of a liquid (which are much closer together than those of a gas). Both cohesion and molecular interchange contribute to liquid viscosity.

The impact of increasing the temperature of a liquid is to reduce the cohesive forces while simultaneously increasing the rate of molecular interchange.

The former effect causes a decrease in the shear stress while the latter causes it to increase. The result is that liquids show a reduction in viscosity with increasing temperature. With high temperatures, viscosity increases in gases and decreases in liquids, the drag force will do the same.

Impact of Increasing Temperature

The impact of increasing temperature will be to slow down the sphere in gases and to accelerate it in liquids. When you consider a liquid at room temperature, the molecules are tightly bound together by attractive inter-molecular forces (e.g. Van der Waal forces).

It is these attractive forces that are responsible for the viscosity since it is difficult for individual molecules to move because they are tightly bound to their neighbors.

The increase in temperature causes the kinetic or thermal energy to increase and the molecules become more mobile.

The attractive binding energy is reduced and therefore the viscosity is reduced. If you continue to heat the liquid the kinetic energy will exceed the binding energy and molecules will escape from the liquid and it can become a vapor.

This information has been sourced, reviewed and adapted from materials provided by Fungilab.

For more information on this source, please visit Fungilab.

 

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Fungilab. (2020, February 18). How does Temperature Change Viscosity in Liquids and Gases?. AZoM. Retrieved on February 29, 2020 from https://www.azom.com/article.aspx?ArticleID=10036.

  • MLA

    Fungilab. "How does Temperature Change Viscosity in Liquids and Gases?". AZoM. 29 February 2020. <https://www.azom.com/article.aspx?ArticleID=10036>.

  • Chicago

    Fungilab. "How does Temperature Change Viscosity in Liquids and Gases?". AZoM. https://www.azom.com/article.aspx?ArticleID=10036. (accessed February 29, 2020).

  • Harvard

    Fungilab. 2020. How does Temperature Change Viscosity in Liquids and Gases?. AZoM, viewed 29 February 2020, https://www.azom.com/article.aspx?ArticleID=10036.

Comments

  1. Ajit Rai Ajit Rai India says:

    Is there an exception or any cases where the viscosity of gases reduces as the temperature increases?

    • Behrooz Nabavi Behrooz Nabavi Iran says:

      if  the temperature of gas exceeds  the ionization temperature, the viscosity will be reduced. for example >10000 K for Ar.

  2. Anironi Mitra Anironi Mitra United States says:

    how does viscosity of liquids vary with pressure

    • Saurabh Thakur Saurabh Thakur United States says:

      Except water the viscosity of liquid incrases with increase in pressure

  3. Saurabh Thakur Saurabh Thakur United States says:

    Viscosity is proportional to square root then how viscosity increases because value in square root increases then whole value decrases

  4. Nikita Suponya Nikita Suponya United States says:

    Can someone please explain why the viscosity of gases increases with increasing temperature (opposite behavior of fluids).  Is this because the cohesive forces of gases are not as prevalent as that of fluids, and therefore the molecular interchange forces dominate viscous adhesion?  As in, the increased kinetic energy of gas molecules promotes the interaction and adhesion of valence electrons with neighboring molecule nuclei... which causes the increases in shear stress.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit