The Nature of Liquids

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The Nature of Liquids
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Liquids

• The ability of gases and liquids to flow allows
  then to conform to the shape of their
  containers.
• Liquids are much more dense then gases.

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More on liquids.

• Increasing the pressure on a liquid has hardly
  any effect on its volume. (The same is true of
  solids).
• For that reason, liquids and solids are known as
  condensed states of matter.

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Key Concept!!!

• The interplay between the disruptive motions of
  particles in a liquid and the attractions among
  the particles determines the physical properties
  of liquids.

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Evaporation Vaporization

• The conversion of a liquid to a gas or vapor is
  called vaporization.
• When such a conversion occurs at the surface of a
  liquid that is not boiling, the process is called
  evaporation.

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Key Concept

• During evaporation, only those surface molecules
  with a certain minimum kinetic energy can escape
  from the surface of the liquid.

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More on Evaporation.

• Liquid evaporates faster when heated. This is
  because heating a liquid increases the average
  kinetic energy of its particles.
• As evaporation occurs, the particles with the
  highest kinetic energy escape first.
• Evaporation is a cooling process!!

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Vapor Pressure
evaporation
Condensation
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• An increase in temperature of a contained liquid
  increases the vapor pressure.

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Boiling Pointvapor pressure external pressure

• When a liquid is heated to a temperature at which
  particles throughout the liquid have enough
  kinetic energy to vaporize, the liquid begins to
  boil.
• Because atmospheric pressure is lower at higher
  altitudes, boiling points decrease at higher
  altitudes.

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• Although vapor has the same kinetic energy as the
  liquid, its potential (or stored energy) is much
  higher.
• Thus a burn from steam is more severe than one
  from an equal mass of boiling water at the same
  temperature.

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The Nature of Solids

• The general properties of solids reflect the
  orderly arrangement of their particles and the
  fixed locations of their particles.

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Melting Point
Melting
Freezing
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Crystal Structure

• The type of bonding that exists between particles
  in crystals determines their melting points.
• Not all solids melt however.
• Wood and cane sugar for example, decompose when
  heated.

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• Allotropes are two or more different molecular
  forms of the same element in the same physical
  state.

Diamond
Fullerene
Graphite
Allotropes of Carbon
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• Amorphous Solids lack an ordered internal
  structure.
• Rubber, plastic and asphalt are examples

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Changes of State

• Sublimation is the change of a substance to a
  vapor without passing through the liquid state.

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Phase Diagrams

• A phase diagram gives the conditions of
  temperature and pressure at which a substance
  exists as a solid, liquid and gas (vapor).

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Phase Diagram Cont

• The Triple Point describes the only set of
  conditions at which all three phases can exist in
  equilibrium with one another.
• A decrease in pressure lowers the boiling point
  and raises the melting point
• An increase in pressure will raise the boiling
  point and lower the melting point.