Notes

Outline

Liquids and Solids

T-97 Molecular Comparison of Physical States

Interparticle Forces of Attraction Anion-Cation Ion-Dipole Hydrogen Bonding Dipole-Dipole London Dispersion

Anion-Cation Forces Occur in solid state of Ionic compounds Anions attract Cations Largest force of  Attraction Explains why Ionic Compounds have highest Melting and Boiling Points

Ion Dipole Forces Ionic compound dissolved in a polar solvent Explains high solubility of Ionic compounds in polar solvents like water

Hydrogen Bonding Attraction between Hydrogen and Flourine, Oxygen, or Nitrogen atom Occurs only in molecules that have a Hydrogen atom covalently bonded to either Flourine, Oxygen, or Nitrogen atom Explains large boiling points and melting points of compounds having Hydrogen bonded to F, O, or N.

T-11.23   Hydrogen Bonding In Water

Dipole-Dipole Attractions Polar molecules attracting one another Explains high solubility of polar substances dissolved in other polar substances

T-11.19  Alignment of polar H-Cl molecules

London Dispersion Forces One molecule’s positive nucleii attracting a neighboring molecules electrons Produces an induced dipole Only forces of attraction of non-polar molecules All molecules have weak London Dispersion forces Explains the low boiling points and melting points of non-polar substances

T-98    London Dispersion Forces

Boiling Points vs Intermolecular Forces Increasing total intermolecular forces increases boiling points

T-99 Boiling Points of Hydrides

T-100 Flow Chart of Intermolecular Forces

Viscocity of Liquids Viscocity-Internal resistence of molecules flowing past each other Increases with Increasing Intermolecular Forces Relative viscocity can be measured with Pipet and stopwatch Viscometer-Instrument measuring absolute viscocity

Surface Tension of Liquids Surface Tension-Energy required to expand the surface area of a liquid by a unit amount Adhesive vs cohesive forces If adhesive forces of container surface greater than cohesive forces between molecules then surface curves downward (concavity) If adhesive forces are less than cohesive forces then surface curves upward (convexity) Only noticeably observed when liquid confined to narrow diameter

T-11.3  Intermolecular Forces Affect On Physical Properties

Heat of Fusion\ Heat of Fusion- Energy required (endo) to melt a solid at its constant melting point. Specific Heat of Fusion- Heat of Fusion on a per  gram basis Molar Heat of Fusion- Heat of Fusion on a per mol basis Energy required for melting (mass) ( specific Heat of Fusion) (mols) ( Molar Heat of Fusion) The reverse process is Heat of solidification(exo)

Heat of Vaporization of Liquid Heat of vaporization-Energy required (endo) to convert a liquid to a vapor at the boiling point Specific Heat of vaporization Molar Heat of Vaporization The reverse process os Heat of Condensation (exo)

Heat of Sublimation Heat of sublimation- Energy required(endo) to sublimate a solid to a vapor Heat of Deposition is the reverse process(exo)

T-101 Heating Curve

Problem Involving Heating Curve

Critical Temperature and Pressure Critical Temperature- Temperature above which a gas cannot be liquified at any pressure Critical Pressure-The only pressure that will liquify a gas

Dynamic Equilibrium Two opposing processes that occur simultaneously at equal rates From a macrocosmic view the equilibrium state appears static From a microcosmic(molecular) view the equilibrium is changing Example of chipped crystal immersed in a saturated solution

Vapor Pressure Vapor Pressure- The pressure of a vapor in equilibrium with the liquid state Factors Influencing Vapor Pressure Increasing molecular mass (size) decreases vapor pressure (Increased molecular forces) Increasing Temperature increases vapor pressure(Increased Kinetic Energy overcoming molecular forces)

Boiling Point of Liquids Boiling Point-Temperature at which the vapor pressure of a liquid becomes equal to the external pressure

T-102 Vapor Pressure vs Temperature

Factors Affecting the Boiling Point of a substance External Pressure-Increasing the pressure increases Boiling Point Example-Reduced Pressure  Distillation Impurities-Increases Boiling Point

Factors Affecting Boiling Point Between Substances Molecular Size-Increases the molecular forces between molecules leads to higher Boiling Point Structure- Branching reduces molecular forces and decreases Boiling Point Molecular Forces-Graeter the forces the higher the Boiling Point

Estimating Boiling Points Using Vapor Pressure Curves Do Problem

T-102 Vapor Pressure Curve

Phase Diagrams Boiling Point Curve (boundary) Melting Point Curve Sublimation Point Curve Triple Point Critical Points

T-103 General Phase Diagram

Specific Phase Diagrams Water Carbon Dioxide

T-104 Phase Diagrams of Water and Carbon Dioxide