CHM1046 Final Exam Study Guide 1 Chapter 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 boundary Intermolecular Forces • Intermolecular Forces: Attractive forces between molecules o Much weaker o Ex) 41 kJ to vaporize 1 mole of water • Intramolecular Forces: Hold atoms together in a molecule o Much stronger o Ex) 930 kJ to break all O-H bonds in 1 mole of water • Measures of Intermolecular Force: o Boiling point o Melting point o ∆Hvap o ∆Hfus o ∆Hsub Polar 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 bond In 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 moleculesCHM1046 Final Exam Study Guide 2 • 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 molecules o Applies to all o Usually increase with molar mass • Polarizability: The ease with which the electron distribution in the atom or molecule can be distorted o 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 #11.1 o 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 #11.2 o Which of the following can form hydrogen bonds with water? CH3OCH3 • Yes CH4 • No F2 • YesCHM1046 Final Exam Study Guide 3 HCOOH • Yes Na+ • No Intermolecular Forces: Strongest Weakest 1. Ion-Dipole: Ion + polar molecule 2. Hydrogen bond: O-H, F-H, or N-H + O, N, or F 3. Dipole-dipole: Polar + polar 4. Ion-induced dipole: Ion + nonpolar 5. Dipole-induced dipole: Polar + nonpolar 6. Dispersion forces: All Properties of Liquids • Surface Tension: The amount of energy required to stretch or increase the surface of a liquid by a unit area o 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 flow o 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 pointCHM1046 Final Exam Study Guide 4 Vapor Pressure versus Temperature • Practice Problem #11.7 o 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 external pressure is 1 atmCHM1046 Final Exam Study Guide 5 • 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 a liquid 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 pointCHM1046 Final Exam Study Guide 6 Heating Curve Solid-Gas Equilibrium • Molar Heat of Sublimation (∆Hsub): The energy required to sublime 1 mole of a solid o ∆Hsub = ∆Hfus + ∆Hvap Hess’s Law • Practice Problem #11.8 o 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 gasCHM1046 Final Exam Study Guide 7 Phase Diagram of Water Phase Diagram of Carbon Dioxide Effect of Increase in Pressure on the Melting Point of Ice and the Boiling Point of WaterCHM1046 Final Exam Study Guide 8 Chapter 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 Interaction o Solute-Solute Interaction o Solvent-Solute InteractionCHM1046 Final Exam Study Guide 9 “Like dissolves like” • Two substances with similar intermolecular forces are likely to be soluble in each other o Nonpolar molecules are soluble in nonpolar solvents CCl4 in C6H6 o Polar molecules are soluble in polar solvents C2H5OH in H2O o Ionic compounds are more soluble in polar solvents NaCl in H2O or NH3 (l) • Practice Problem #12.1 o 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
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