intermolecular forces: phases of matter & colligative properties
DESCRIPTION
Intermolecular Forces: Phases of Matter & Colligative Properties. Dr. Ron Rusay. Changes of State Phase transitions Phase Diagrams Liquid State Pure substances and colligative properties of solutions Solid State Classification of Solids by Type of Attraction between Units - PowerPoint PPT PresentationTRANSCRIPT
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Intermolecular Forces: Phases of Matter & Colligative Properties
Dr. Ron Rusay
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• Changes of State– Phase transitions– Phase Diagrams
• Liquid State– Pure substances and colligative properties of solutions
• Solid State– Classification of Solids by Type of Attraction between
Units– Crystalline solids; crystal lattices and unit cells– Structures of some crystalline solids– Determining the Crystal Structure by X-ray Diffraction
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Phase Transitions• Melting: change of a solid to a
liquid.
• Freezing: change a liquid to a solid.
• Vaporization: change of a solid or liquid to a gas. Change of solid to vapor often called Sublimation.
• Condensation: change of a gas to a liquid or solid. Change of a gas to a solid often called Deposition.
H2O(s) H2O(l)
H2O(l) H2O(s)
H2O(l) H2O(g)
H2O(s) H2O(g)
H2O(g) H2O(l)
H2O(g) H2O(s)
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Phases of Matter / Intermolecular Forces
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Phase Changes
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QUESTION
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Bonds vs. Intermolecular Forces
16 kJ/mol
431 kJ/mol
(150 - 1000 kJ/mol) (Ionic bond 700-4,000 kJ/mol)
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Ion-Dipole Forces (40-600 kJ/mol)• Interaction between an ion and a dipole (e.g. NaOH and
water = 44 kJ/mol)• Strongest of all intermolecular forces.
Intermolecular Forces
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Dipole-Dipole Forces(permanent dipoles)
Intermolecular Forces
5-25 kJ/mol
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Dipole-Dipole Forces
Intermolecular Forces
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London or Dispersion Forces• An instantaneous dipole can induce another dipole in an
adjacent molecule (or atom).• The forces between instantaneous dipoles are called
London or Dispersion forces ( 0.05-40 kJ/mol).
Intermolecular Forces
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London Dispersion Forces
Intermolecular Forces
Which has the higherattractive force?
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London Dispersion Forces
Intermolecular Forces
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Gecko: toe, setae, spatulae6000x Magnification
http://micro.magnet.fsu.edu/primer/java/electronmicroscopy/magnify1/index.html
Geim, Nature Materials (2003) Glue-free Adhesive100 x 10 6 hairs/cm2
Full et. al., Nature (2000)5,000 setae / mm2
600x frictional force; 10-7 Newtons per seta
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Boiling Points &Hydrogen Bonding
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Hydrogen Bonding
• Hydrogen bonds, a unique dipole-dipole (10-40 kJ/mol).
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Which pure substances will not form hydrogen bonds?
I) CH3CH2OH II) CH3OCH3
III) H3C−NH−CH3 IV) CH3F
A) I and II B) I and III C) II and III D) II and IV
QUESTION
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Hydrogen Bonding
Intermolecular Forces
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DNA: Size, Shape & Self Assemblyhttp://www.umass.edu/microbio/chime/beta/pe_alpha/atlas/atlas.htm
Views & Algorithms
10.85 Å10.85 Å
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Intermolecular Forces
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Protein Shape: Forces, Bonds, Self Assembly,Folding
10-40kJ/mol
700-4,000kJ/mol
150-1000kJ/mol
0.05-40kJ/mol
Ion-dipole(Dissolving)40-600kJ/mol
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Predict which liquid will have the strongest intermolecular forces of attraction (neglect the small differences in molar masses).
A) CH3COCH2CH2CH3 (molar mass = 86 g/mol)
B) CH3CH2CH2CH2CH2OH (molar mass = 88 g/mol)
C) CH3CH2CH2CH2CH2CH3 (molar mass = 86 g/mol)
D) HOH2C−CH=CH−CH2OH (molar mass = 88 g/mol)
QUESTION
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Vapor Pressure on the Molecular Level
Vapor Pressure
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Explaining Vapor Pressure on a Molecular LevelVapor Pressure
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Volatility, Vapor Pressure, and Temperature
Vapor Pressure
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QUESTION
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Temperature Dependence of Vapor Pressures
• The vapor pressure above the liquid varies exponentially with changes in the temperature.
• The Clausius-Clapeyron equation shows how the vapor pressure and temperature are related.
CT1
RTH
Pln vap +×Δ
−=
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Clausius – Clapeyron Equation
• A straight line plot results when ln P vs. 1/T is plotted and has a slope of ΔHvap/R.
• Clausius – Clapeyron equation is true for any two pairs of points.
⎟⎟⎠⎞
⎜⎜⎝⎛
−×Δ
=21
vap
1
2T1
T1
RTH
PP
ln
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QUESTION
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Energy of Heat and Phase Change• Heat of vaporization: heat
needed for the vaporization of a liquid.H2O(l) H2O(g) ΔH = 40.7 kJ/mol
• Heat of fusion: heat needed for the melting of a solid.H2O(s) H2O(l) ΔH = 6.01 kJ/mol
• Temperature does not change during the change from one phase to another.
50.0 g of H2O(s) and 50.0 g of H2O(l) were mixed together at 0°C. Determine the heat required to heat this mixture to 100.0°C and evaporate half of the water.
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Phase Diagrams• Graph of pressure-temperature
relationship; describes when 1,2,3 or more phases are present and/or in equilibrium with each other.
• Lines indicate equilibrium state between two phases.
• Triple point- Temp. and press. where all three phases co-exist in equilibrium.
• Critical temp.- Temp. where substance must always be gas, no matter what pressure.
• Critical pressure- vapor pressure at critical temp.
• Critical point- system is at its critical pressure and temp.
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Phase Diagrams
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Phase Diagrams
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The Phase Diagrams of H2O and CO2
Phase Diagrams
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Published by AAAS
S. H. Oh et al., Science 330, 489-493 (2010)
Oscillatory Vapor-Liquid-Solid growth of sapphire nanowires (α-Al2O3)
660°C, Pressure = 10–6 Pa
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Critical Temperature and Pressure
Phase Changes
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QUESTION
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Pressure Effects
Factors Affecting Solubility
gg kPS =
If Sg is the solubility of a gas, k is a constant, and Pg is the partial pressure of a gas, then Henry’s Law gives:
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QUESTIONA minimum of 1.3 10–4 M O2 must be maintained in freshwater supplies to sustain aquatic life. In the mountains of Montana, the partial pressure of O2 may drop to 0.15 atm. What is the water concentration of O2 there? Henry’s constant for O2 = 1.3 10–3
mol/L-atm. At the lower elevations at the base of those mountains, would more or less O2 be dissolved in water?
A. M = 2.0 10–4; more dissolvedB. M = 8.7 10–4; more dissolvedC. M = 2.0 10–4; less dissolvedD. M = 8.7 10–4; less dissolved
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Phase Diagrams for Pure Water (Red) and for an Aqueous Solution Containing a Nonvolatile
Solute (Blues)
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Sugar Dissolved in Water to Make Candy Causes the Boiling Point to be Elevated
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Spreading Salt on a Highway
The Addition of Antifreeze Lowers the Freezing Point of Water in a Car's Radiator
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• Colligative properties depend on quantity and type of solute/solvent molecules. (E.g. freezing point depression and melting point elevation.)
Lowering Vapor Pressure• Non-volatile solvents reduce the ability of the surface
solvent molecules to escape the liquid.• Therefore, vapor pressure is lowered.• The amount of vapor pressure lowering depends on the
amount of solute.
Colligative Properties
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Lowering Vapor Pressure• Raoult’s Law: PA is the vapor pressure with solute, PA
is the vapor pressure without solvent, and A is the mole fraction of A, then
• Recall Dalton’s Law:
Colligative Properties
€
PA = ΧA P°A
€
PA = ΧA Ptotal
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QUESTION
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Molality and Molarity
• Molality relates to colligative properties.• Converting between molarity (M) and molality (m)
requires density.• Therefore Molarity and molality are most often not equal
Concentration
solvent of kgsolute moles Molality, =m
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QUESTION
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QUESTIONHousehold bleach is an aqueous solution of sodium hypochlorite. If 5.25 g of NaOCl (molar mass = 74.5 g/mol) were placed in 94.75 g of water, what would you calculate as the molality? The density of the solution is slightly greater than water. Would the molarity of the solution be greater, less or the same as the molality?
A. 0.0705 m; M would be greaterB. 0.705 m; M would be the sameC. 0.744 m; M would be greaterD. 0.744 m; M would be less
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Molal Boiling-Point Elevation Constants (Kb) and Freezing-Point Depression Constants (Kf)
for Several Solvents
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QUESTIONSuppose you want to keep the water in your car cooling system from freezing during a cold Alaska winter night. If you added 5.00 Kg of ethylene glycol (C2H4(OH)2 mm = 62.0 g/mol) to5.50 kg of water, what would be the freezing temperature of the coolant/water mixture in your automobile?
k f.p. H2O = –1.86°C kg/ mol
A. –0.0367°CB. –7.90°CC. –14.7°CD. –27.3°C
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Atomic Solid / Ionic Solid / Molecular Solid
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Structure of Solids• Types of solids:
– Crystalline – a well defined arrangement of atoms; this arrangement is often seen on a macroscopic level.• Ionic solids – ionic bonds hold the solids in a regular three
dimensional arrangement.• Molecular solid – solids like ice that are held together by
intermolecular forces.• Covalent network – a solid consists of atoms held together in
large networks or chains by covalent networks.• Metallic – similar to covalent network except with metals.
Provides high conductivity. – Amorphous – atoms are randomly arranged. No order
exists in the solid.
Structure of Solids
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• Crystals are made up of atoms in regular arrays – the smallest of repeating array of atoms is called the unit cell.
• There are 14 different unit cells that are observed which vary in terms of the angles between atoms some are 90°, but others are not.
Unit Cells
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• Length of sides a, b, and c as well as angles a, b, g vary to give most of the unit cells.
Unit Cells
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Closest Packing Arrangement of Uniform Sphere
• Arrays of atoms act as if they are spheres. Two or more layers produce a 3-D structure.
• Angles between groups of atoms can be 90° or can be in a more compact arrangement such as the hexagonal closest pack (see below) where the spheres form hexagons.
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Hexagonal Closest Packed Structure
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Hexagonal Close Packed: The Red Sphere has 12 Nearest Neighbors
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Consider an interior atom in the simple cubic crystal lattice. What is the maximum number of unit cells that share this atom in the three-dimensional crystal lattice?
A) 2 B) 4 C) 6 D) 8
QUESTION
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• Face Centered Cubic structure has a-b-c-a-b-c stacking. It takes three layers to establish the repeating pattern and has 4 atoms per unit cell and the coordination number is 12.
Unit Cells
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The Net Number of Spheres in a Face-Centered Cubic Unit Cell
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• Simple-cubic• Body-centered cubic• Face-centered cubic
Unit Cells
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The number of atoms per unit cell in the body-centered cubic lattice is
A) 1 B) 2 C) 3 D) 4
QUESTION
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• Simple-cubic shared atoms are located only at each of the corners. 1 atom per unit cell.
• Body-centered cubic 1 atom in center and the corner atoms give a net of 2 atoms per unit cell.
• Face-centered cubic corner atoms plus half-atoms in each face give 4 atoms per unit cell.
Unit Cells
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X-ray Crystallographyhttp://info.bio.cmu.edu/courses/03231/ProtStruc/ProtStruc.htm
Rosalind Franklin’s Photo 51
http://molvis.sdsc.edu/pdb/dna_b_form.pdb
46 Å
12 base sequence
(1953-2003)