Properties of Liquids• Kinetic-Molecular theory …The phase of any substance is determined

by the inter and intramolecular forces present and the KE of the molecules. – KE = intermolecular forces– Most liquids are made of molecules

• their intramolecular forces are covalent in nature. • The strength of the intermolecular forces determine the physical properties of the

liquid.

Basic Properties

• definite volume • conforms to the shape of its container • not compressible • elements and molecules are not in fixed

positions

Evaporation vs Vaporization• Within a liquid, molecules are free to move. The rate of movement at the surface

is related to the KE of the system. • Evaporation occurs when molecules at the surface overcome the attractive force

of liquid and leave as gas – the rate of evaporation is directly related to the temperature – in a closed container, the rate of evaporation is equal to the rate of condensation

(returning to liquid) • Vaporization occurs when a liquid completely turns to gas

– vapor pressure is the pressure exerted above a liquid as molecules leave in the gaseous form • vapor pressure and temperature are directly related • the boiling point of a solution occurs when the vapor pressure of the liquid is equal to the

atmospheric pressure • normal boiling point is defined as the temp at which the vapor pressure = atmospheric at 101.3kPa

(1atm)

Viscosity• Viscosity is a term used to describe the fluid friction (resistance to

flow) within a fluid. The amount of viscosity is completely dependent on the amount and strength of the intermolecular bonds. – Substances with large amounts of H bonds are very viscous – Temperature and viscosity are inversely related (low temp = high viscosity)

Surface Tension• Surface tension is the downward (toward the middle) force that a fluid exerts

on its surface molecules. It is responsible for giving drops their round appearance. The rules governing surface tension are the same as for viscosity.– Substances with large amounts of H bonds have high surface tensions – Temperature and surface tension are inversely related (low temp = high surface

tension) – Surface tension determines the boiling point of a liquid

Other "Unusual" Properties of Water• Extremely high boiling point - due to its shape • High specific heat - can absorb great amounts of heat without a great

increase in temp. • The density in solid form is less than its liquid phase • Very high surface tension • Very high heat of vaporization (boiling point) • Is the universal solvent