Effect of Pressure on Viscosity - QS Study
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Effect of pressure on viscosity

We see that there is effect of pressure on the co-efficient of viscosity of liquids, if pressure increases; the co-efficient of viscosity also increases.

Explanation: As the pressure increases the intermolecular distance decreases; consequently, intermolecular force increases. As a result, the relative velocity between two adjacent layers decreases, hence co-efficient of viscosity increases. For ideal gases, viscosity depends only on temperature. For real gases, that’s still a very good approximation. For liquids, changing the pressure does very little unless you increase the pressure a lot.

Pressure have effect on both, viscosity of liquid as well as gases.

  • On increasing pressure viscosity of liquid molecules increases due to the increase in the resistance to flow of liquid.
  • On increasing pressure the viscosity of gas molecules decreases due to the increase in glow of molecules. Under most conditions, viscosity is independent of pressure. Viscosity has a pressure dependence for gases when the ideal gas model breaks down (e.g. at low temperatures and/or high pressures) and for liquids at very high pressure.

There is no effect of pressure on the co-efficient of viscosity of gases. For most circumstances near the conditions we live in, pressure doesn’t have much effect on viscosity.