Ch. 10 States of Matter

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Ch. 10 States of Matter

• Ch. 10.1 The Nature of Gases
• Ch. 10.2 The Nature of Liquids
• Ch. 10.3 The Nature of Solids
• Ch. 10.4 Changes of State

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Ch. 10.1 The Nature of Gases

• Kinetic theory
• States that the tiny particles in all forms of
  matter are in constant motion
• Makes 3 basic assumptions
• Gases are composed of tiny particles with very
  little volume and a great deal of empty space
  between them no attractive forces
• The particles move rapidly in random motion they
  travel independently in straight paths and
  collisions occur
• All collisions are perfectly elastic total
  kinetic energy is conserved

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Ch. 10.1 The Nature of Gases

• Gas pressure
• Force exerted by a gas per unit surface area
• Atmospheric pressure
• Results from the collisions of air molecules with
  objects
• Decreases as you move higher in the atmosphere
• Barometers are used to measure atmospheric
  pressure (dependent on weather)
• SI unit is the pascal (Pa) two older units are
  mm HG and atm
• One standard atm is the pressure necessary to
  support 760mm Hg in a mercury barometer at 25oC

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Ch. 10.1 The Nature of Gases

• Gas pressure
• Modern barometers are aneroid
• Measure the of collisions of air molecules
• It is important to measure gases under a standard
  condition
• STP is defined as OoC and 101.3kPa or 1 atm
• Kinetic energy and Kelvin temperature
• When heated, particles absorb some energy as
  potential, the rest is kinetic and speeds up the
  particles
• Particles have varying amounts of energy, so
  average kinetic energy is used
• At absolute zero, 0 K, the motion of particles
  theoretically ceases
• This has never been achieved in a lab

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Ch. 10.2 The Nature of Liquids

• A model for liquids
• Particles that make up a liquid vibrate and spin
  as they move from place to place
• this motion contributes to the kinetic energy
• Most particles do not have enough energy to
  escape the intermolecular forces and enter the
  gaseous state
• Liquids and solids are known as the condensed
  states of matter

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Ch. 10.2 The Nature of Liquids

• Evaporation
• Conversion of a liquid to a gas or vapor is
  called vaporization
• When the process occurs in a liquid that is not
  boiling, it is called evaporation
• Liquid particles with enough kinetic energy break
  away from the surface and enter the gas phase
• Some particles collide with air molecules and
  return to the liquid phase
• Liquids evaporate faster when heated
• Evaporation is a cooling process
• When particles with high kinetic energy escape,
  the overall energy of the liquid is lowered

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Ch. 10.2 The Nature of Liquids

• Evaporation in a closed container has different
  results
• Particles that escape collide with the walls if
  the container and produce a vapor pressure
• the pressure of the gas above the liquid
• Particles will continue to leave the liquid, but
  some will re-enter
• A dynamic equilibrium exists (see pg. 276)
• Rate of evaporation rate of condensation
• Increasing temperature increases the vapor
  pressure

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Ch. 10.2 The Nature of Liquids

• Vapor pressure can be measured with a manometer
• Boiling point
• The temperature at which the vapor pressure of a
  liquid is equal to the external pressure
• Normal boiling point occurs under standard
  pressure
• Boiling occurs more easily at high altitudes, and
  more slowly at low altitudes
• Boiling is also a cooling process
• The temperature never rises above boiling point
• Liquids can only boil faster if heat increases
• Vapor pressure is at the same temperature, but it
  has a much higher potential energy

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Ch. 10.3 The Nature of Solids

• A model for solids
• Particles in solids tend to vibrate about a fixed
  point
• They are dense and incompressible
• They do not flow or take the shape of their
  containers
• Melting point
• When solids are heated, the particles gain
  kinetic energy
• Organization of the particles is disrupted
• The melting point is the temperature at which a
  solid becomes a liquid
• Disruptive vibrations overcome the strong forces
  holding the particles together
• Melting and freezing are reverse processes

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Ch. 10.3 The Nature of Solids

• Crystal structure and unit cells
• Crystals have sides or faces
• There are 7 types of crystal systems
• The shape of a crystal depends on the arrangement
  of the particles
• The smallest group of particles within the
  crystal system is called a unit cell
• There are 3 types of unit cells
• Some substances can take more that one crystal
  form these are called allotropes

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Ch. 10.3 The Nature of Solids

• Amorphous solids
• Not all solids are crystalline, some are
  amorphous
• their atoms are randomly arranged
• Rubber, plastic and asphalt are amorphous solids
• Glass is another type
• Sometimes called supercooled liquids
• Structure is intermediate between a crystalline
  solid and a free-flowing liquid
• Does not melt, but gradually softens
• Breaks in irregular shapes

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Ch. 10.4 Changes of State

• Phase diagrams
• Give the conditions of temperature and pressure
  at which a substance exists as a solid, liquid
  and gas
• The point at which all three curves meet is known
  as the triple point
• Sublimation
• Change of state from a solid to a gas without
  passing through the liquid phase
• Solids have a vapor pressure
• If the vapor pressure is high enough, a solid can
  change directly to a gas
• Dry ice (solid CO2), and mothballs (naphthalene)
  are examples