CHAPTER 11 INTERMOLECULAR FORCES AND LIQUIDS AND SOLIDS 11 2 Intermolecular Forces Intermolecular forces attractive forces between molecules Intramolecular forces attractive forces within molecules o Intermolecular forces are weaker than intramolecular forces Van der Waals Forces Dipole Dipole Forces Ion Dipole Forces Dispersion Forces o Dipole dipole dipole induced dipole and dispersion forces o Attractive forces between polar molecules o Attractive forces between a polar molecule and an ion o Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules o Induced dipoles caused by a separation of positive and negative charges in a nonpolar molecule in the proximity of an ion or a polar molecule o Exist in all compounds Polarizability o The larger number of electrons the greater the polarizability Increase with molar mass Hydrogen bond fluorine o The strongest bond after ion ion bonds o Attractive forces between hydrogen and either nitrogen oxygen or o The boiling point of HF is lower than water because each H2O takes part in four intermolecular hydrogen bonds 11 3 Properties of Liquids Surface tension the amount of energy required to stretch or increase the surface of a liquid by a unit area o Stronger intermolecular forces greater surface tension Viscosity measure of a fluid s resistance to flow o Stronger intermolecular forces greater viscosity 11 4 Crystal Structure Amorphous structure without a specific structure Crystalline solid a structure where atoms molecular or ions occupied specific positions o Ice Unit cell a basic repeating structure of a crystalline solid o Simple cubic cell Basic repeating unit in an array of spheres o 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 of a liquid Phase changes transformations from one phase to another Molar heat of vaporization Hvap energy required to vaporize 1 mole 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 solid CHAPTER 12 PHYSICAL PROPERTIES OF SOLUTIONS 12 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 solution o 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 solvent 12 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 temperature 12 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 solution o c kP c mol L k mol L atm P atm o Volume goes up pressure goes down o Pressure goes up volume goes down 12 6 Colligative Properties of Nonelectrolyte Solutions Four colligative properties o 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 point of 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 one o Semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules possibly dependent on atomic size o Osmotic pressure symbol pi the pressure required to stop osmosis o pi MRT M mol L R 0 0821 L atm mol K T K 12 7 Colligative Properties of Electrolyte Solutions Van t Hoff factor o 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 KINETICS 13 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 time 13 3 The Relation Between Reactant Concentration and Time First order reaction a reaction whose rate depends on the reactant concentration raised to the first power o 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 life 13 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 rate o 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 spent CHAPTER 14 CHEMICAL EQUILIBRIUM 14 1 The Concept of Equilibrium and the Equilibrium Constant Chemical equilibrium is achieved when the rates of the forward and reverse reactions are equal and the concentrations of the products and reactions remain constant The magnitude of the constant tells us whether the reaction favors the o Denoted by K products or reactants o K
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