CHM1046Chapter 11: Intermolecular Forces, Liquids, and Solids- Phase: Homogeneous part of the system in contact with other parts of the system,but separated from them by a well-defined boundaryIntermolecular Forces- Intermolecular Forces: Attractive forces between moleculeso Much weakero Ex) 41 kJ to vaporize 1 mole of water- Intramolecular Forces: Hold atoms together in a moleculeo Much strongero Ex) 930 kJ to break all O-H bonds in 1 mole of water- Measures of Intermolecular Force:o Boiling pointo Melting pointo ∆Hvapo ∆Hfuso ∆HsubPolar Molecules and Dipole Moments- Polar Molecule: Electrons spend more time in the vicinity of one atom than the other atoms- Dipole Moment: The measure of the polarity of a bondIn an H-F molecule, the electrons spend more time near the fluorine atom than the hydrogen because the fluorine is more electronegative- Dipole-Dipole Forces: Attractive forces between polar molecules1CHM1046- Ion-Dipole Forces: Attractive forces between an ion and a polar molecule- Dispersion Forces: Attractive forces that arise as a result of temporary dipoles induced in atoms or moleculeso Applies to all o Usually increase with molar mass- Polarizability: The ease with which the electron distribution in the atom or molecule can be distortedo Increases with: Greater number of electrons More diffuse electron cloud- Hydrogen Bond: A special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom-Practice Problem #11.1o What type(s) of intermolecular forces exist between the following pairs? HBr and H2S- Dipole-dipole- Dispersion Cl2 and CBr4- Dispersion I2 and NO3-- Ion-induced dipole- Dispersion NH3 and C6H6- Dipole-induced dipole- Dispersion-Practice Problem #11.2o Which of the following can form hydrogen bonds with water? CH3OCH3- Yes CH4- No F2- Yes2CHM1046 HCOOH- Yes Na+- NoIntermolecular Forces: Strongest Weakest 1. Ion-Dipole: Ion + polar molecule2. Hydrogen bond: O-H, F-H, or N-H + O, N, or F3. Dipole-dipole: Polar + polar4. Ion-induced dipole: Ion + nonpolar5. Dipole-induced dipole: Polar + nonpolar6. Dispersion forces: AllProperties of Liquids- Surface Tension: The amount of energy required to stretch or increase the surface of a liquid by a unit areao Strong intermolecular forces high surface tension- Cohesion: The intermolecular attraction between like molecules- Adhesion: An attraction between unlike molecules- Viscosity: A measure of a fluid’s resistance to flowo Strong intermolecular forces high viscosity- Equilibrium Vapor Pressure: The vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation- Molar Heat of Vaporization (∆Hvap): The energy required to vaporize 1 mole of liquid at its boiling point3CHM1046Vapor Pressure versus Temperature-Practice Problem #11.7o Diethyl ether is a volatile, highly flammable organic liquid that is used mainly as a solvent. The vapor pressure of diethyl ether is 401 mmHg at 18 º C. Calculate its vapor pressure at 32 º C. P2 = 657 mmHg- Boiling Point: Temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure- Normal Boiling Point: The temperature at which a liquid boils when the externalpressure is 1 atm4CHM1046- Critical Temperature (Tc): The temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure- Critical Pressure (Pc): The minimum pressure that must be applied to bring about liquefaction at the critical temperature- Solid-Liquid Equilibrium: The melting point of a solid or the freezing point of aliquid is the temperature at which the solid and liquid phases coexist in equilibrium- Molar Heat of Fusion (∆Hfus): The energy required to melt 1 mole of a solid substance at its freezing point5CHM1046Heating CurveSolid-Gas Equilibrium- Molar Heat of Sublimation (∆Hsub): The energy required to sublime 1 mole of a solido ∆Hsub = ∆Hfus + ∆Hvap Hess’s Law-Practice Problem #11.8o Calculate the amount of energy (in kilojoules) needed to heat 346 g of liquid water from 0 º C to 182 º C. Assume that the specific heat of water is 4.184 J/g º C over the entire liquid range, and that the specific of steam is 1.99 J/g º C. 985 kJ- Phase Diagram: Summarizes the conditions at which a substance exists as a solid, liquid, or gas6CHM1046Phase Diagram of WaterPhase Diagram of Carbon Dioxide7CHM1046Effect of Increase in Pressure on the Melting Point of Ice and the Boiling Point of WaterChapter 12: Physical Properties of Solutions- Solution: A homogenous mixture of 2 or more substances- Solute: The substance(s) present in smaller amounts- Solvent: The substance present in the larger amount- Saturated Solution: Contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature- Unsaturated Solution: Contains less solute than the solvent has the capacity to dissolve at a specific temperature- Supersaturated Solution: Contains more solute than is present in a saturated solution at a specific temperature- Three types of interactions in the solution process:o Solvent-Solvent Interactiono Solute-Solute Interactiono Solvent-Solute Interaction8CHM1046“Like dissolves like”- Two substances with similar intermolecular forces are likely to be soluble in each othero Nonpolar molecules are soluble in nonpolar solvents CCl4 in C6H6o Polar molecules are soluble in polar solvents C2H5OH in H2Oo Ionic compounds are more soluble in polar solvents NaCl in H2O or NH3 (l)-Practice Problem #12.1o Predict the relative solubilities in the following cases: Bromine (Br2) in benzene (C6H6, µ = 0 D) and in water (µ = 1.87 D)- C6H6 (nonpolar) KCl in carbon tetrachloride (CCl4) and in liquid ammonia (NH3)- NH3 (polar) Formaldehyde (CH2O) in carbon disulfide (CS2, µ = 0 D) and in water- WaterConcentration Units- Concentration: The amount of solute present in a given quantity of solvent or solution9CHM1046-Practice Problem #12.2o A sample of 0.892 g of potassium chloride (KCl) is dissolved in 54.6 g of water. What is the percent by mass of KCl in the solution? 1.61%-Practice Problem #12.3o Calculate the molality of a sulfuric acid solution containing 24.4 g of sulfuric acid in 198 g of water. The molar mass of sulfuric acid 98.09 g. 1.26 m-Practice Problem #12.4o The density of a 2.45 M aqueous solution of methanol (CH3OH) is 0.976 g/mL.
View Full Document
Unlocking...