Liquids and Solids

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• Liquids and Solids

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Properties of Liquids and the Kinetic-Molecular
Theory

• Liquid- is a form of matter that has a definite
  volume and takes the shape of its container. The
  particles are in constant motion.
• The intermolecular forces in liquids can be
  dipole-dipole, London dispersion, and hydrogen
  bonding.
• The Kinetic-Molecular Theory states that
  particles of a liquid have no fixed space, and
  move about constantly.
• Fluid-is a substance that can flow and takes the
  shape of its container- used for liquids and
  gases both
• (Showing meting of ice and changes in molecular
  structure)
• http//mutuslab.cs.uwindsor.ca/schurko/animations/
  waterphases/status_water.htm

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Liquids molecular structure
http//www.media.pearson.com.au/schools/cw/au_sch_
whalley_sf1_1/int/matter.html (magnification at
molecular level from ice to water)
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Properties of Liquids
Relatively High Density The liquids are very dense because the particles of liquids are extremely close together. Also, different liquids have different densities.
Relative Incompressibility Liquids are much less compressible because they have tightly packed particles, and also transmit pressure equally.
Ability to Diffuse The liquids diffuse with most liquids, but at a slower rate than gases because the particles are more tightly packed, and there are many attractive forces between the particles.
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Intermolecular ForcesVan Der Waals Forces

• Significant in molecular substances (gases, most
  liquids and solids that are molecular)
• Strong intermolecular forces lead to increased
  m.p. and b.p.
• What are some properties of molecular substances?
  (nonconductors, insoluble in water, but soluble
  in most non polar solvents)

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LDFs-temporary dipole interactions and are the
weakest intermolecular bonds-present between all
molecules and non bonded atoms, and are
significant in noble gas atoms and non polar
compounds.-The strength of LDFs depends upon two
things1. of e in atoms that make up the
molecule2. The ease with which e are dispersed
to form temporary dipoles.
http//antoine.frostburg.edu/chem/senese/101/liqui
ds/faq/h-bonding-vs-london-forces.shtml Dipole-Dip
ole, LDFs animation
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Dipole-Dipole Interactions

• Found in PC molecules. Stronger than LDFs
• LDFs and Dipole-Dipole are also called as Van Der
  Waals forces
• Ex ICl

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H Bonds

• When H is bonded to a relatively small,
  electronegative atom, such as N,O, or F
• Strongest of the weak interactions (strongest
  intermolecular forces)

• animation

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Properties of Liquids Surface Tensionhttp//www.
visionlearning.com/library/module_viewer.php?mid5
7Water Strider Video
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Surface Tension and Capillary Action

• Surface Tension-a force that tends to pull
  adjacent parts of a liquids surface together,
  thereby decreasing surface area to the smallest
  possible size.
• The higher the attraction forces (intermolecular
  forces), the higher the surface tension. Surface
  tension causes liquid droplets to take a
  spherical shape.
• Capillary action- the attraction of the surface
  of a liquid to the surface of a solid.
• Capillary action is the reason water from the
  roots of a tree goes to the leaves. It is also
  responsible for the liquid surface called the
  meniscus.

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Surface Tension

• The surface of any liquid behaves as if it was a
  stretched membrane. This phenomenon is known as
  surface tension
• Surface tension is caused by intermolecular
  forces at the liquids interface with a gas or a
  solid.
• Surface tension depends on the nature of the
  liquid, the surrounding media and temperature.
• Liquids that have strong intermolecular forces
  will have higher values of surface tension than
  liquids that have weak intermolecular forces.

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http//citt.ufl.edu/Marcela/Sepulveda/html/en_tens
ion.htm
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Viscosity

• Defined as resistance to flow of a fluid.
• Viscous liquids move slower.
• The greater the intermolecular forces the more is
  the viscosity.
• http//plc.cwru.edu/tutorial/enhanced/lab/visco/in
  tro/intro.htm (Viscosity and molecular size
  interactive simulation)
• http//www.youtube.com/watch?v7Ft9VDDPWb4feature
  related (video on different density liquids)

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Physical Properties of Water

• Highest density at 4 degrees celsius. Ice is one
  of the few solids to have a lower density in
  solid phase as compared to liquid phase. This
  property is very useful in ice skating, and
  fishes in lakes etc.
• Because of H Bonding water has a much higher b.p.
  and m.p.as compared to other liquids. This
  property is making water one of the best
  coolants.
• ( Ex Perspiration, In car radiators etc)

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Reversible Change

• Some changes and reactions are reversible
• They go forward (to the right) A B ? C D
• and backwards (to the left) A B ? C D

• Written with a two-way arrow

A B ? C D
Examples

• Boiling condensing
• Freezing melting
• Recharging a rechargeable battery

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Chemical Equilibrium

• For a reversible reaction, when the forward
  rate equals the
  backward rate, a chemical equilibrium, has
  been established.
• Both the forward and backward reactions
  continue, but there is a balance of products
  un-reacting and reactants reacting.

A B ? C D
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• Ex Change of state liquid? ? gas. IF temp and
  volume stay the same.

Evaporation(forward rate) decreases
Forward rate Backward rate
condensation (backward rate) increases
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• Le Chateliers Principle is about reducing
  stress a stress applied to a chemical
  equilibrium

If a stress is applied to a system in dynamic
equilibrium, the system changes in a way that
relieves the stress
(1850 1936)
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Stress Change Temperature

• Ex liquid heat energy ?? vapor
• This reaction is endothermic ( absorbs heat
  energy) in the forward direction.
• Stress Result

Increase T Forward rxn favored shifts forward to
reduce extra heat until new equilibrium is
reached where concentration of vapor is higher.
.
Decrease T Backward rxn favored shifts
backward to replace lost heat (exo). Vapor
conc. lower than original.
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Liquid- Vapor Equilibrium

• Vapor Pressure The pressure exerted on the
  surface of a liquid by the vapor that is in
  equilibrium with the liquid is called as vapor
  pressure
• Once equilibrium between a liquid and vapor is
  reached, the number of molecules per unit volume
  in a vapor does not change with time. Hence, the
  vapor pressure over the liquid remains constant
  at a given temperature.
• Vapor Pressure is independent of the volume of
  the container. Why?
• http//www.mhhe.com/physsci/chemistry/essentialche
  mistry/flash/vaporv3.swf
• (vapor pressure equilibrium on manometer)

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Vapor Pressure Vs. TemperatureVapor pressure
increases with the increase in temperature.(VP
vs Temp)

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Evaporation

• Vaporization-the process by which a liquid or
  solid changes to gas.
• Evaporation- is the process where particles
  escape from the surface of a non boiling liquid
  and enters the gas state.
• Evaporation takes place because the particles of
  liquids have different kinetic energies,
  therefore some of the particles with higher
  kinetic energy overcome the intermolecular forces
  and evaporate to go in the gas phase.

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Boiling

• Boiling- is the change of a liquid to bubbles or
  vapor. Boiling occurs when the vapor pressure
  becomes equals atmospheric pressure.
• A liquid boils at the temp. at which its vapor
  pressure is equal to the pressure above its
  surface. (usually atmospheric pressure)
• If the pressure above the liquids surface is 1
  atm, then this temperature is called as its
  Normal Boiling Point
• B.P. of a liquid is reduced by lowering the
  pressure above it.
• Why does it take longer to cook at high altitudes?

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Boiling A liquid boils at a temp. when the vapor
pressure P1 becomes equal to the external
pressure P2 above the liquid
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Phase Changes

• Melting(fusion)/Freezing
• Vaporization/Condensation
• Sublimation/Deposition
• http//hogan.chem.lsu.edu/matter/chap26/animate3/a
  n26_035.mov
• (s-l-g with molecular motion at phase change)

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Time Temperature Curve movie 1 3 H m DT
Cp
2 4 H m DHvap

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Boiling
Condensation
T
Melting(Fusion)
0
Freezing
1 2 3 4
Time ( heat energy added ) song
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Solids
High Density and Incompressibility Solids are much more dense than liquids or gases because their particles are so much closer together. Solids are also less compressible than liquids, and are mostly thought of as not compressible at all.
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Types of Solids

• Solids are of two types
• Crystalline solids- consist of crystals which are
  substances which are organized in symmetric,
  geometric ways.
• Amorphous solids-non crystalline solid where the
  particles are arranged randomly.

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Differences between Amorphous and Crystalline
Solids

• Crystalline Solids
• Exist either as single crystals or group of
  crystals fused together.The total three
  dimensional arrangement of particles is called as
  crystal structure.
• Crystalline solids can be of four types
• Ionic, Covalent Network, Metallic and Covalent
  Crystals

• Amorphous Solids
• Unlike crystalline solids, amorphous solids do
  not have a regular shape, there are no strong
  intermolecular forces. so particles are not
  arranged in any particular order.
• Ex Plastic, Glasses

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Crystalline Solids

• There are four types of crystals
• 1. Ionic crystals The positive and negative ions
  crystals have properties including high melting
  points, hard and brittle, and good insulators.
• 2. Covalent network crystals the sites have
  single atoms. They are nonconductors or
  semiconductors and have high melting points. Ex
  Graphite, diamond
• 3. Metallic crystals these are metal atoms
  with a sea of valence electrons. There is high
  electric conductivity of metals, and the melting
  points differ. Ex Iron, Aluminum etc
• 4. Covalent molecular crystals they are held
  together by covalent forces, and have low melting
  points, are easily vaporized, soft, and good
  insulators. Ex Sugar, Dry Ice

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Crystalline Solids
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Covalent Network Diamond
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Covalent Network Graphite
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CHANGES IN STATE
Liquid
1 atm
P
Solid
Gas
O T, in C 100
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