FSU CHM 1046 - CHAPTER 11: INTERMOLECULAR FORCES

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CHAPTER 11: INTERMOLECULAR FORCES AND LIQUIDS AND SOLIDS11.2 Intermolecular Forces- Intermolecular forces: attractive forces between molecules- Intramolecular forces: attractive forces within moleculeso Intermolecular forces are weaker than intramolecular forces- Van der Waals Forceso Dipole-dipole, dipole-induced-dipole, and dispersion forces- Dipole-Dipole Forceso Attractive forces between polar molecules- Ion-Dipole Forceso Attractive forces between a polar molecule and an ion- Dispersion Forceso Attractive forces that arise as a result of temporary dipoles induced in atoms or moleculeso Induced dipoles caused by a separation of positive and negative charges in a nonpolar molecule in the proximity of an ion or a polar moleculeo Exist in all compounds- Polarizabilityo The larger number of electrons, the greater the polarizability “Increase with molar mass”- Hydrogen bondo The strongest bond after ion-ion bondso Attractive forces between hydrogen and either nitrogen, oxygen orfluorine.o The boiling point of HF is lower than water because each H2O takes part in four intermolecular hydrogen bonds11.3 Properties of Liquids- Surface tension: the amount of energy required to stretch or increase the surface of a liquid by a unit areao Stronger intermolecular forces = greater surface tension- Viscosity: measure of a fluid’s resistance to flowo Stronger intermolecular forces = greater viscosity11.4 Crystal Structure- Amorphous structure: without a specific structure- Crystalline solid: a structure where atoms, molecular or ions occupied specific positionso Ice- Unit cell: a basic repeating structure of a crystalline solido Simple cubic cell Basic repeating unit in an array of sphereso Face-centered cubic cell A sphere at the center of each six faces of the cube, in addition to eight corner spheres Equivalent of 4 spheres: (1/2 x 6 face + 1/8 x 8 corners = 4)o Body-centered cubic cell: On center sphere and eight shared corner spheres Equivalent of 2 spheres: (1 x 1 body + 1/8 x 8 corners = 2)11.8 Phase Changes- Phase changes: transformations from one phase to another- Molar heat of vaporization (∆Hvap): energy required to vaporize 1 mole of a liquid- Molar heat of fusion (∆Hfus): energy required to melt 1 mole of a solid- Boiling point: the temperature at which the vapor pressure of a liquid is equal to the external pressure- ∆Hsub: energy required to sublime (solid to gas) 1 mole of a solidCHAPTER 12: PHYSICAL PROPERTIES OF SOLUTIONS12.1 Types of Solution- Solution: a homogeneous mixture of two or more substances- 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 it has the capacity to dissolve- Supersaturated solution: contains more solute than is present in a saturated solutiono Crystallization: the process in which dissolved solute comes out of solution and forms crystals (precipitate)12.3 Concentration Units - Percent by mass: the mass of a solute to the mass of a solution, multiplied by 100%- Mole fraction: (ex.) X mol / (X+Y) mol- Molarity: the number of moles of solute in 1 L of solution- Molality: the number of moles of solution per kg of solvent12.4 The Effect of Temperature on Solubility- In most cases, the solubility of a solid increases with temperature- In most cases, the solubility of gases in water decreases with increasing temperature- Because volume is affected by temperature, molarity may also change with temperature12.5 The Effect of Pressure on the Solubility of Gases- Henry’s Law: the solubility of a gas in a liquid is proportional to the pressure of the solutiono c = kP  c = mol/L, k = mol/L*atm, P = atmo Volume goes up, pressure goes downo Pressure goes up, volume goes down12.6 Colligative Properties of Nonelectrolyte Solutions- Four colligative propertieso Boiling point elevation, freezing point depression, osmotic pressure and vapor-pressure lowering- Raoult’s Law states that the partial pressure of a substance A over a solution is equal to the partial pressure (XA) of A times the vapor pressure of pure A. - Boiling point elevation (∆Tb): boiling point of solution minus boiling pointof the pure solvent- Freezing point depression (∆Tf): freezing point of solution minus boiling point of the pure solvent- Osmosis: the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated oneo Semipermeable membrane: allows the passage of solvent molecules but blocks the passage of solute molecules, possibly dependent on atomic sizeo Osmotic pressure (symbol: pi) the pressure required to stop osmosiso pi = MRT M = mol/L, R = 0.0821 L*atm/(mol*K), T = K12.7 Colligative Properties of Electrolyte Solutions- Van’t Hoff factoro i = # of particles in sol’n after dissociation/ # of formula units initially dissolved in sol’n Depends on ionic compounds NaCl, i = 2 (1Na+, 1Cl-) Na2SO4, i = 3 (2Na+, 1SO4^2-)CHAPTER 13: CHEMICAL KINETICS13.1 The Rate of a Reaction Chemical kinetics is concerned with the speed at which reactions occur Reaction rate: the change in concentration of a reactant or product over time13.3 The Relation Between Reactant Concentration and Time First-order reaction: a reaction whose rate depends on the reactant concentration raised to the first powero A plot of ln [M] vs t will serve a straight line unique to first-order reactions Second-order reaction: a reaction who rate depends on the concentration of one reactant raised to the second power, or the concentration of two different reactants, each raised to the first power Reaction Half-life13.4 Activation Energy and Temperature Dependence of Rate Constants Rate = number of collisions/s Activation energy: the minimum amount of energy required to initiate a chemical reaction Activated complex: transition state; a temporary species formed by reactant molecules as a result of the collision before they form the product Increase in temperature = increase in molecule speed = increased energy in collision = increase in rateo Arrhenius equation Plot of lnk vs 1/T gives a straight line with slope = -Ea/R R = 8.314 J/(K*mol)13.6 Catalysis Catalyst: a substance that increases the rate of a reaction by lowering the activation energy without being spentCHAPTER 14: CHEMICAL EQUILIBRIUM14.1 The Concept of Equilibrium and the Equilibrium Constant Chemical


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FSU CHM 1046 - CHAPTER 11: INTERMOLECULAR FORCES

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