Solid, Liquid, and Gas

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Solid, Liquid, and Gas
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GAS LIQUID SOLID
Kinetic Energy Winnings
Intermolecular Forces Winning
Disorder
Order
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The state of matter, depends on two things

• Kinetic Energy which increases as a substance
  is heated. Brings disorder, and leads in the
  direction of randomness of chaos.
• Intermolecular Forces the forces between the
  molecules that make up the substances. Tends to
  bring order to the movements of molecules.

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Solid, Liquid, Gas
(a) Particles in solid (b) Particles in
liquid (c) Particles in gas
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Energy Changes Accompanying Phase Changes
Gas
Condensation
Vaporization
Sublimation
Deposition
Energy of system
Liquid
Melting
Freezing
Solid
Brown, LeMay, Bursten, Chemistry 2000, page 405
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Solid (metal crystals)
A solid is a form that has definite shape and
volume. Metals and ionic substances have high
melting and boiling points (usually) The
particles are tightly packed together and have
very orderly arrangements. Solids expand only
when heated.
H2O(s) Ice
Zumdahl, Zumdahl, DeCoste, World of Chemistry
2002, page 31
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Liquid
In a liquid

• molecules are in
• constant motion
• there are appreciable
• intermolecular forces
• molecules are close
• together but as the
• distance increases
• order decreases.
• Liquids are almost
• incompressible

In a liquid, there is short-range order, and
long-range disorder.
Zumdahl, Zumdahl, DeCoste, World of Chemistry
2002, page 31
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Gas
Similar to a liquid, Gas takes the shape of the
container. Unlike a liquid, gas can expand to
fill any volume. Particles tend to be sparse
and far apart and constantly changing Gas vs.
Vapor Gas is used for substances that exist
in a gaseous state at room temperature.
Vapor describes the gaseous state of a substance
that is usually a liquid or solid at room temp.
H2O(g) Steam
Zumdahl, Zumdahl, DeCoste, World of Chemistry
2002, page 31
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Gas, Liquid, and Solid
Gas
Liquid Solid
Zumdahl, Zumdahl, DeCoste, World of Chemistry
2002, page 441
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Some Properties of Solids, Liquids, and Gases
(The difference in spacing and
speed are the main reason for the different
properties.
Property Solid Liquid
Gas
Amt of order Very Orderly Short-range
order Almost complete Long-range
disorder disorder Shape Fixed Shape
of container No shape Position of Particle
Fixed, no movement Some movement
Always moving
Compressibility Very low Very Low
High Arrangement of Fixed, very
close Random, close Random, far
apart Particles Conduction of heat Metals
and graphite Metals very good Very poor
very good
others poor others poor. Interactions between
Very strong Strong Essentially
none particles
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Comparing Boiling Melting Points

• The higher the relative molecular mass, the
  higher the melting point and the higher the
  boiling point.
• a. The greater the mass of a molecule, the more
  electrons it possesses. Thus, as the molecules
  get heavier, the instantaneous dipole forces
  become greater.
• 2. Where melting or boiling points are higher
  than expected, look for very strong
  intermolecular forces, especially H-Bonds.

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States of Matter
Gas
Solid
Liquid
heat
heat
Holds Shape Fixed Volume
Shape of Container Free Surface Fixed Volume
Shape of Container Volume of Container
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Liquids boil when its vapor pressure equals
atmospheric pressure
The two key properties we need to describe
are EVAPORATION and its opposite CONDENSATION
add energy and break intermolecular bonds
EVAPORATION
CONDENSATION
release energy and form intermolecular bonds
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Evaporation

• To evaporate, molecules must have sufficient
  energy to break IM forces.
• Molecules at the surface break away and become
  gas.
• Only those with enough KE escape.
• Breaking IM forces requires energy. The process
  of evaporation is endothermic.
• Evaporation is a cooling process.
• It requires heat.

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Condensation

• Change from gas to liquid
• Achieves a dynamic equilibrium with vaporization
  in a closed system.
• What is a closed system?
• A closed system means matter cant go in or
  out. (put a cork in it)
• What the heck is a dynamic equilibrium?

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Dynamic Equilibrium

• When first sealed, the molecules gradually escape
  the surface of the liquid.
• As the molecules build up above the liquid - some
  condense back to a liquid.
• The rate at which the molecules evaporate and
  condense are equal.

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Dynamic Equilibrium

• As time goes by the rate of vaporization remains
  constant but the rate of condensation increases
  because there are more molecules to condense.
• Equilibrium is reached when the rate at which
  molecules leave the liquid equals the rate at
  which molecules join the liquid.

• Rate of Vaporization Rate of Condensation
• The equilibrium vapor pressure is the vapor
  pressure measured when a dynamic equilibrium
  exists between condensation and evaporation

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States of Matter
Solid Liquid crystal fourth state of
matter Liquid Gas
Images MacDonald, R. Liquid Crystals -
Fascinating State of Matter or "Soft is
beautiful". Accessed 7-2006
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Liquid Crystals

• A phase of matter similar to a liquid, in which
  the molecules are arranged regularly in one or
  two dimensions
• They are liquids, but they can behave like solids
  at certain ranges of temperature.

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Liquid Crystal Model
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Unique Properties of Liquid Crystals

• The orientation of Liquid Crystals can be
  affected by
• Pressure
• Temperature
• Electrical Field
• The arrangement
• Of molecules can be
• Upset by slight changes in their surroundings.

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Glass

• Allows light to pass through very easily
• Melts over a range of temperatures and remains
  viscous, which allows glass to be blown into
  different shapes or rolled into sheets
• Basic structure is built from Silicon tetraoxide
  and the tetrahedral shape gives glass its high
  viscosity.

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Ideal and Real Gases
They fill all the space open to them They expand
when heated.
They exert a pressure on the walls of their
containers
The pressure changes as the temperature changes
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Key Assumptions of an Ideal Gases

• The molecules has mass, but negligible size
• There are no intermolecular forces
• The collisions between the molecules are
  perfectly elastic (molecules do not change their
  total kinetic energy when they bump into each
  other).

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No Real Gas is Ideal
CH4
N2
2.0
H2
PV nRT
CO2
Ideal gas
1.0
0
0
200
400
600
800
1000
P (atm)
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The Kinetic Theory of Gases
Gases consist of molecules in constant state of
random motion.
The pressure of a gas is due to the collisions of
the molecules with the walls of the container.
The molecules travel in straight lines until they
collide with one another, or with the walls of
the container.
In these collisions, the total kinetic energy of
the molecule does not change.
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Lower Temp (500K)
Number of molecules having a particular speed.
Higher Temp (1000K)
BUT, look here, you will notice They are not
symmetrical the curve stretches out more at
higher than at lower energies.
Kinetic Energy of Molecules
As the temp. goes up, the average energy of all
the molecules increase, but the distribution of
spreads, and therefore kinetic energy, spreads
out.
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Pressure and Volume of Ideal Gases

• The pressure of gas is caused by the collisions
  of the molecules with the walls of containers.
• Pressure of an ideal gas depends on 3 factors
• of molecules per unit volume
• The mass of the molecules
• Their speed

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Ideal Gas Law
PV nRT
Brings together gas properties.
Can be derived from experiment and theory.
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Ideal Gas Equation
Universal Gas Constant
Volume
P V n R T
Pressure,
Temperature
No. of moles
P pressure in pascals, Pa V volume, in
m3 T temperature (Kelvin) n number of
moles R 8.314 JK-1mol-1
Kelter, Carr, Scott, Chemistry A Wolrd of Choices
1999, page 366
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P pressure in pascals, Pa - Pressure is
often quoted in kilopascals, kPa, where 1 kPa
103 Pa - Atmosphere is an old unit, 1atm
100kPa V volume, in m3 - 1m3 1 x 103 dm3
1 x 106cm3 - 1 litre 1 dm3 1000 cm3 1 x
10-3 m3 T temperature (Kelvin) n number
of moles R 8.314 JK-1mol-1
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Example Problem
What is the volume of 0.582mol of a gas at 15oC
and 81.8kPa?