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Viscosity Liquids exhibit viscosity. Viscosity = resistance to flow Viscosity depends on strength of intermolecular forces sizes & shapes of molecules temperature The stronger the intermolecular forces, the higher the viscosity. As temperature , viscosity . As temperature , viscosity .
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The Nature of Liquids
Properties of LiquidsProperties of Liquids
Definite volumeIndefinite shapeParticles are close together, but they can move
a little bit… so liquids can flow.
Density of liquids is much greater than gases. Ex: DH2O(l) is 1250X greater than DH2O(g) at 25C.
Liquids can be compressed… but change in volume is very slight and requires enormous pressure.
Viscosity
Liquids exhibit viscosity. Viscosity = resistance to flow
Viscosity depends on strength of intermolecular forces sizes & shapes of molecules temperature
The stronger the intermolecular forces, the higher the viscosity. As temperature , viscosity . As temperature , viscosity .
Viscosity and Molecular Shape
(a) Carbon tetrachloride, CCl4, consists of small, symmetrical molecules with fairly weak intermolecular forces. It has a low viscosity.
(b) Octadcane, C18H38, consists of long molecules with fairly strong intermolecular forces. It has a relatively high viscosity.
• Need a thin film of oil on bearing surfaces to prevent flaking of metal.
• If the oil is too thick, it won’t circulate at low temperatures.
• If the oil is too thin, it will lose film strength at high temperatures.
Oil in an engine prevents direct metal to metal contactOil in an engine prevents direct metal to metal contact..
Where does the Where does the marble drop marble drop fastest?fastest?
Slowest?Slowest?
water
glycerol
Surface Tension
Particles at the surface of a liquid exist in an unbalancedunbalanced environment. No attraction from above to balance attractions from below.
Net attractive force pulling down.
Surface seeks smallest possible area.
Surface Tension
Energy required to increase the surface area by a given amount
Measure of inward pull
Strong intermolecular attractions
Surfactants
Compounds that lower the surface tension of water
Disrupt hydrogen bonds between H2O molecules.
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Capillary Action
Water forms a concave meniscus in a glass tube.
Attractive forces between water and glass greater than the attractive forces between the water molecules.
Upward movement of a liquid in a narrow tube is called capillary actioncapillary action.
Cohesive and Adhesive Forces
Cohesive forces are forces of attraction between molecules of a liquid.
Adhesive forces are forces of attraction between molecules of a liquid and another substance.
Meniscus
Force (Hg-glass) Force (Hg-Hg)
Force (H2O-glass) Force (H2O- H2O)
