CHEM 135 1st Edition Exam 1 Study Guide Lectures 1 10 Lecture 1 January 21 Chapter 11 Intermolecular Forces electrostatic attractive forces that exist between molecules weaker than bonding forces farther apart and not sharing electrons molecules with stronger IMFs have higher BP Dispersion Forces Ion Dipole Dipole Dipole o Hydrogen Bonding Instantaneous dipole can induce dipoles in other molecules Ex Identify the molecule with dipole dipole forces a CO2 b CH3Cl c CH4 d HI Determine the kind of IMF present in each compound a N2 b NH3 c Co d CCl4 Lecture 2 January 23 Dispersion and thermal behavior based on molar mass Mostly the higher the molar mass greater the dispersion forces also meaning a higher boiling point o Ex He molar mass 4 00 g mol BP 4 2 K and Ar molar mass 39 95 g mol BP 87 K Dispersion and thermal behavior based on shape This only applies when molar masses are identical The greater the contact surface area means greater dispersion forces resulting in a higher boiling point Liner molecules tend to have higher boiling points versus circular due to this concept Breakdown of Intermolecular Forces Type Present In Dispersion All molecules and atoms Dipole Dipole Polar molecules Hydrogen Bonding Molecules containing H bonded to N O or F Ion Dipole Mixtures of ionic compounds and polar compounds Strength 1 4 4 strongest 1 2 3 4 Ex Place the following compounds in order of increasing strength of intermolecular forces CH4 CH3CH2CH3 CH3CH3 Place the following compounds in order of decreasing strength of intermolecular forces HF H2 CO2 Surface Tension the tendency of liquids to minimize the surface area Stronger IMF results in higher degrees of surface tension Molecules at the surface are less stable Liquids like to take the shape with the least geometrical area to minimize surface area Viscosity the resistance of a liquid to flow Stronger IMF greater the viscosity Phase Changes Gas to liquid condensation exo Liquid to gas vaporization endo Liquid to solid freezing exo Solid to liquid melting fusion endo Solid to gas sublimation endo Gas to solid deposition exo Lecture 3 January 26 Review the phase diagram know how to read one and know these terms associated with them Area only one phase can exist Line two phases can co exist Triple point three phases can co exist Critical point vapor and liquid not distinguishable Solids Crystal Lattice and unit cell Lattice regular 3 D arrangement of atoms within a crystalline solid Unit Cell smallest repeating unit of lattice All about cubic unit cells All 90 angles between corners of the unit cell The length of all edges are equal For an atom in a unit cell o 1 8 of each corner atom is within the unit cell o of each atom on a face is within the unit cell o of each atom on an edge is within the unit cell o 1 of each atom inside the unit cell is within the unit cell Simple Cubic Cell SCC SCC 1 atom 1 8 x 8 corner atoms 1 atom Body Centered Cubic Cell BCC BCC 2 atoms 1 8 x 8 corner atoms 1 atom 1 atom in the center Face Centered Cubic Cell FCC FCC 4 atoms 1 8 x 8 corner atoms 1 atom 1 2 x 6 face atoms 3 atoms Classification of crystalline solids Molecular Solids o Composite units are molecules ice Ionic Solids o Composite units are formula units cations and anions salt Atomic Solids o Composite units are atoms Nonboding held together by dispersion forces solid xenon Metallic held together by metallic bonds gold Lecture 4 January 28 Solution a homogeneous mixture of two or more substances Solvent the majority component of a solution Solute the minority component of a solution Enthalpy of the solution Hsolution Hsolute Hsolvent Hmix H1 Separation of solute molecules the enthalpy needed for separation is positive making this separation endothermic due to the energy required to break the bonds within the solute molecules H2 Separation of solvent molecules Again separation enthalpy endothermic reaction H3 Formation of solute solvent interactions The formation of new bonds enthalpy due to the energy being released exothermic reaction Exothermic solution formation Hsolute Hsolvent Hmix releasing heat Endothermic solution formation Hsolute Hsolvent Hmix absorbing heat Saturated solution contains max amount of solute cannot dissolve any more solute if added Unsaturated solution contains less solute than the max capacity can dissolve more solute Supersaturated solution contains more solute then the max capacity contains excess undissolved solute Solubility Solubility the amount of solute that can dissolve in a given amount of solvent at a given temperature When most solids are placed in water solubility increases as temperature increases o Why Bonds break easier when heated allowing for the solute to dissolve faster Solubility of a gas in a liquid increases with increasing pressure of the gas above the liquid o Henry s Law Sgas kHPgas Colligative Properties These are properties that depend ONLY on the number not the type of solute particles in a solution o Vapor Pressure Lowering o Freezing Point Depression o Boiling Point Elevation o Osmotic Pressure Vapor Pressure and Dynamic Equilibrium Dynamic equilibrium rate of evap rate of condensation Vapor Pressure Pressure of a gas in dynamic equilibrium with its liquid Ex If a non volatile liquid doesn t evaporate easily solute is added to a liquid what happens o Vapor pressure of solution is lowered Raoult s Law Vapor Pressure of the solution is given by Psolution Xsolvent P solvent Xsolvent mole fraction of the solvent n solvent n solute n solvent Vapor pressure lowering P P Xsolvent P solvent Lecture 5 January 30 Freezing point depression and boiling point elevation The freezing point of a solution is lower than the freezing point of the pure solvent Tf m Kf The boiling point of a solution is higher than the boiling point of the pure solvent Tb m Kb m molality of a solution in moles solute per kilogram solvent Kf Kb freezing point depression and boiling point elevation constants Ex 1 Calculate the freezing point of a 1 7 m aqueous glycol solution 2 What mass of ethylene glycol C2H6O2 in grams must be added to 1 0 kg of water to produce a solution that boils at 105 0 C Lecture 6 February 2 Osmosis is the flow of solvent from a solution of low concentration into a solution of high concentration Osmotic Pressure The amount of pressure needed to keep osmotic flow from taking place ie Osmotic pressure PREVENTS osmosis from occurring MRT osmotic pressure is directly proportional to the molarity of the solute M