Solids and Liquids

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Solids and Liquids

• Chapters 16 and 17

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Kinetic Theory of Matter

• Gas Solid Liquid

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Kinetic Theory of Gases

• Particles are independent from one another and
  move in straight lines.
• Change of direction occurs only when particles
  strike each other or container.
• Movement is random.

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Kinetic Theory of Liquids

• Particles much closer together.
• Particles do not act independently from one
  another.
• Have a vibratory type of motion.
• Movement occurs when particles shift between the
  spaces of particles.

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Kinetic Theory of Solids

• Particles close together and do not act
  independently.
• Particles occupy a relatively fixed position in
  relation to surrounding particles.
• Vibration around a fixed point.

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Properties of Solids

• All true solid substances are composed of
  crystals.
• Solids have low kinetic energy.
• They have a definite volume and assume their own
  shape.
• High densities and Melting points.

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Crystal Structure

• Crystals are made from small units called unit
  cells.
• These units are repeated over and over again as
  the crystal grows.
• The arrangement of these unit cells is determined
  by the bonds between the particles.
• Early crystallographers classified crystals on
  the basis of their external shapes into seven
  crystal systems.

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Crystal Systems

• Refer to page 398 in text.
• EX Cubic Hexagonal

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• Cubic

• Hexagonal

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Allotropes

• Allotropes are different chemical states of same
  element in same physical state.
• EX Allotropes of carbon are diamonds and
  graphite.
• Diamond cubic lattice held together by strong
  covalent bonds.
• Graphite layers of hexagonal units held
  together by weak forces.

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• Diamond Graphite

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Amorphous Substances

• Amorphous substances, sometimes referred to as
  amorphous solids, appear to be in the solid state
  but have no crystal structure.
• Glass is the best known example.
• Glass does not have a sharply defined melting
  point (like other solids).
• Viscosity (resistance to flow) is used to
  describe the texture of glass.
• High viscosity, high resistance to flow (thick).

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Properties of Liquids

• Liquids occupy a definite volume but they do not
  have their own shape.
• Liquid movement is considered fluid.
• Bodies of nonmoving liquids are always flat on
  top.

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Surface Tension and Capillary Action

• A liquid molecule is attracted to other liquid
  molecules. This is called cohesion.
• Surface tension is a function of cohesion.
• A liquid molecule can also be attracted to other
  materials. This is called adhesion.
• Capillary action is a function of adhesion.

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Surface Tension

• Surface tension is the force at the surface of a
  liquid due to the cohesive forces of the
  molecules of liquid for each other and adhesive
  forces of the liquid molecules for the walls of
  the container.

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• A paper clip will float on water despite having a
  higher density.
• The cohesive forces of the water molecules keep
  the paper clip from pushing through.

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Gerris remigis takes a walk
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Capillary Action

• Capillary action is related to the adhesive
  properties of liquids.
• Liquid molecules are attracted to the straw. As
  they climb up the straw, other molecules
  follow.

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• Capillary action is limited by gravity and the
  size of the straw.
• The thinner the straw or tube the higher up
  capillary action will pull the liquid.

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Intermolecular Forces

• Intermolecular forces are called Van Der Waals
  forces .
• These forces are strongest in liquids and solids.
  (Remember gases have little or no attraction for
  other gas molecules)
• There are three such types of Van Der Waals
  forces

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• London Dispersion Forces (LDF) which are forces
  that exist between elements or nonpolar molecules
  as a result of positive nuclei of one molecule
  attracting the electrons of another molecule. All
  molecular substances exhibit London Forces which
  are the weakest of the Van Der Waals forces.
• EX O2, CH4, Kr

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• 2. Dipole-Dipole interactions which are forces
  that exist between polar molecules where the
  positive end of one molecule attracts the
  negative end of another molecule. Only polar
  molecules can exhibit this type of Van Der Waals
  forces which is considered the second strongest.
• EX HBr, CH3Cl, CO, PCl3, C12H22O11

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• 3. Hydrogen bonding interactions are forces that
  exist between molecules that have a hydrogen atom
  bonded to a highly electronegative atom such as
  Oxygen, Nitrogen, or Fluorine. This represents a
  strong polarity that will have the Hydrogen end
  (positive) attracting the negative end (O,N, or
  F) of other molecules. This type of Van Der Waals
  force represents the strongest type.
• Alcohols are considered Hydrogen bonding
  because of the OH group.
• EX H20, NH3, HF, CH3OH

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Identify the IMF Force

• Must do Lewis Structures (Bonding Unit, Steps
  1-9) to determine polarity of molecules
• Ar
• CCl4
• HF
• NCl3
• C6H11OH
• C6H12O6
• NH3
• CO2

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Ranking Strength of IMFs

• When determining the strength of IMF forces when
  comparing different substances, follow these
  guidelines
• Identify type of force for each substance.
• Ionic bonds are not considered to be an IMF but
  you will often see them. Ionic bonds are stronger
  than IMFs.
• Make subcategories of hydrogen bonded,
  dipole-dipole, and LDF.

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• 4. Rank according to that order. If presented
  with more than one substance in a category follow
  these guidelines
• Hydrogen Bonded the greater the
  electronegativity difference between atoms, the
  stronger the force.
• Dipole-Dipole Same as hydrogen bonded. Look at
  electroneg difference.
• LDF Calculate molar mass of each substance.
  The greater the molar mass, the stronger the
  force.

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• Rank the following set of substances in order of
  increasing strength of IMF.
• H2, H2O, CO, CO2, NH3, SO3, KCl, Br2, NCl3

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IMFs and Boiling and Melting Points (phase
changes)

• There is a relationship between Intermolecular
  forces and Boiling and Melting points of
  substances (all phase changes EX evaporation).
• The stronger the IMF, the higher the Boiling and
  Melting points are.
• It takes more energy (temperature) to overcome
  the force created by the IMF.

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• Identify which substance out of each pair has the
  higher boiling point
• O2 or CO
• H2O or HBr
• HF or CH4
• C6H12O6 or C12H22O11
• PCl3 or NO
• HF or NH3

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Phase Changes

• Phase changes are due to changes in temperature,
  which affects kinetic energy, or pressure, which
  establishes how close the molecules of a
  substance are.

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Heating and Cooling Curves

• Heating Curve

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• Cooling Curve

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Phase Diagrams

• Phase diagrams show how the states of matter in a
  system are affected by changes in temperature and
  pressure.

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• This phase diagram shows the relative
  temperatures and pressures at which each of the
  three states of matter can exist.
• Note the point labeled triple point.
• This is the point at which all three states can
  exist in equilibrium.

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Phase Diagram for CO2
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Equilibrium

• Equilibrium is the state in a system in which
  there is no net change in that system.
• In a state change system, for example, a beaker
  of water that is closed off will have two phases.
• 1. Liquid
• 2. Gas
• The point at which there is no increase in the
  gas particles or no increase in the liquid
  particles is called equilibrium.

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• Molecules sublimating Molecules condensing

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Le Chateliers Principle

• If stress is applied to a system at equilibrium,
  the system will tend to readjust so that the
  stress is reduced. (for chemical reactions)
• The stress may be a temperature, pressure,
  concentration of products or reactants, or other
  external factors.
• Equilibrium shifts occur after a stress has been
  applied.
• Stress ? Shift ? New equilibrium

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H2O (l) H2O (s)

• If we add heat to this system at equilibrium,
  what will happen?
• Thats right! We call that an equilibrium shift
  to the left because we will form more of the
  substance on the left side of the yield sign.
• If we place this system in a freezer, what type
  of equilibrium shift will occur?

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Shifts

• Shift to the left to make more reactants.
• Everything on the left increases, everything on
  the right decreases.
• Shift to the right to make more products.
• Everything on the right increases and reactants
  decrease.

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Stresses to Equilibrium

• Only gases and aqueous substances can induce a
  stress.
• Addition or elimination of solids or liquids will
  not affect equilibrium. They can however,
  increase or decrease when other stresses occur.

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Changing Concentrations and the Effect on
Equilibrium

• N2(g) H2(g) ?? NH3(g)
• What shift will occur when the NH3 is
  increased?
• What happens to N2, and H2?
• What shift will occur when some H2 is taken out
  of the system?
• What happens to N2, and NH3?
• What shift will occur when some NH3 is taken out
  of the system?
• What happens to N2, H2, and NH3?

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Temperature

• If temp or energy (J, kJ, Cal, kcal) is a
  reactant then the reaction is endothermic
  (requires heat and has a positive value)
• Treat temp as any reactant.
• If temp or energy is a product then the reaction
  is exothermic (releases heat and has a negative
  value)
• Treat as any product.

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• Heats of reactions
• Seen as ?H where the ? refers to change
• A positive () ?H is endothermic and energy
  should be written as a reactant.
• A negative (-) ?H is exothermic and energy should
  be written as a product.
• EX ?H -53 kJ or ?H 53 kJ
• ( or let you know which side to place the
  energy on)

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• N2(g) H2(g) ?? NH3(g) heat
• What shift will occur when heat is added to the
  system?
• What happens to N2, H2, and NH3?
• What shift will occur when some NH3 is taken out
  of the system?
• What happens to temperature?
• What shift will occur when heat is taken away
  from the system?
• What happens to N2, H2, and NH3?

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Pressure

• Applies to gases only.
• If increasing pressure, shift will occur in the
  direction of the least moles.
• EX 2 mol ? 1 mol right shift
• If decreasing pressure, shift will occur in the
  direction of the most moles.
• EX 2 mol ? 1 mol left shift
• If moles are equal then there is no shift and
  everything remains the same.

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• N2(g) H2(g) ?? NH3(g) heat
• What shift will occur when pressure is increased?
• What happens to N2, H2, NH3, and
  temperature?
• What shift will occur when pressure is reduced?
• What happens to N2, H2, NH3, and
  temperature?

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K value

• The equilibrium constant (K) is a unitless
  quantity characterizing a chemical equilibrium in
  a chemical reaction which is a useful tool to
  determine the concentration of various reactants
  or products in a system where chemical
  equilibrium occurs.
• It is only affected by temp changes.
• Use the general equation K products
• reactants

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• Note that during a right shift the concentration
  of products increases while the concentration of
  reactants decrease. Mathematically, this
  increases the K value.
• During a left shift the concentration of the
  reactants increase while the concentration of the
  products decrease, decreasing the K value.

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• Note that during a right shift the concentration
  of products increases while the concentration of
  reactants decrease. Mathematically, this
  increases the K value.
• K products ? numerator reactants
  gets larger
  making K larger

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• During a left shift the concentration of the
  reactants increase while the concentration of the
  products decrease, decreasing the K value.
• K products
• reactants ? denominator gets larger
  making K smaller.

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• A large K value, over 1, indicates that the K
  value favors products.
• A small K, less than 1, indicates that K value
  favors reactants.

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If K gt 1, the reaction is product-favored. There
are more products than reactants at equilibrium
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If K lt 1, the reaction is reactant-favored. There
are more reactants than products at equilibrium.
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• N2(g) H2(g) ?? NH3(g) heat
• What shift will occur when heat is taken out of
  the system?
• What happens to the K value?
• What shift will occur when some NH3 is taken out
  of the system?
• What happens to the K value?
• What shift will occur when heat is added to the
  system?
• What happens to the K value?

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Reaction Rate (Keq)

• To express the reaction rate (Keq) for the
  equilibrium reactions, we use the general
  equation
• mA nB ? sP rQ
• Keq PsQr
• AmBn
  

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• Only the phases of matter (g) and (aq) are placed
  into a K expression.
• Disregard (s) and (l) substances.

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• H2 (g) I2 (g) 2HI (g)
• The K for this reaction is
• Keq HI2
• H2 I2
• If we had values for these molecules, we would
  place the values in this equation.

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H2 (g) I2 (g) 2HI (g)

• EX Calculate Keq if
• H2 0.0050 moles
• I2 0.0035 moles
• HI 0.0050 moles
• Keq 0.00502
  0.0050 0.0035

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