CHEM1312H - Capillary Action, Surface Tension, Viscosity

surface tension def

the resistance of a liquid to increase its surface area

surface tension

-molecules in the interior of a liquid are attracted by IMF’s equally in all directions

-molecules at the surface experience a net inward force that pulls surface molecules toward the interior

-the net inward force tends to pull surface molecules toward the interior reducing the surface area and making molecules pack closer to each other

-this surface of water behaves as an “elastic skin” holding the needle

surface tension is affected by…

IMFs and temperature

Surface tension and IMFs

liquids with stronger IMFs tend to have a higher surface tension than liquids with weaker IMFs

surface tension and temperature

surface tension decreases as temperature increases because IMFs are diminished therefore less work is required to extend the surface of a liquid

capillary action

-the spontaneous rising of a liquid in a narrow tube against gravity

-occurs due to the balance between cohesive and adhesive forces

-the adhesive forces between the liquid and the walls of the tube tend to “pull” the liquid upwards

cohesisve forces

intermolecular forces that exist between molecules of a liquid

adhesive forces

intermolecular forces that exist between molecules and the surface of a tube

meniscus

the curved upper surface of a liquid in a tube

meniscus formation

-water: in a glass tube the meniscus is concave or “U-shaped” because adhesive forces (water) is around the same as cohesive forces (water and glass tube)

-mercury: the meniscus is convex or “inverted U-shaped” because adhesive forces are less than cohesive forces and we can say that “mercury does not wet glass”

Viscosity

-the resistance of liquid to flow

-cohesive forces (IMFs) within a liquid create an internal friction which reduces rate of flow

-viscosity decreases with an increase in temperature

the degree of viscosity is determined by

-IMFs between the molecules of the liquid

-size and shape of the molecules

-temperature