Viscosity
Definition and meaning of Viscosity in chemistry.
Viscosity is the resistance of a fluid to flow or deformation under shear stress. It quantifies how easily molecules can move past one another.
In more detail
Viscosity arises from intermolecular forces creating internal friction as molecules move relative to each other. Temperature strongly affects viscosity: in most liquids it decreases with increasing temperature as molecules gain kinetic energy, while in gases viscosity increases with temperature. Higher viscosity indicates greater resistance to flow, making fluids thicker and slower-moving.
Key facts
| Field | Physical Chemistry |
|---|---|
| SI Unit | Pascal-second (Pa·s) |
| Common Unit | Centipoise (cP) |
| Symbol | η (eta) or μ (mu) |
Water at 20°C has a viscosity of approximately 1.0 centipoise (0.001 Pa·s), while honey is roughly 2,000 to 10,000 centipoise, reflecting its much greater resistance to flow.
Frequently asked questions
Why does viscosity matter in chemistry?
Viscosity affects reaction rates, molecular diffusion, mixing efficiency, and transport phenomena. It is critical in industrial chemical processes, polymer science, and biochemical systems.
How does temperature affect viscosity differently for liquids and gases?
For liquids, higher temperatures decrease viscosity as increased molecular motion overcomes intermolecular forces. For gases, higher temperatures increase viscosity as molecular collisions and momentum transfer increase.