CHEM 112 EXAM 2 CHAPTER 11 Intermolecular Forces Exist between two molecules will not be dealing with INTRA aka ionic covalent IMFs directly relate to physical properties boiling point melting point etc Gas weak IMFs high compressibility Liquid intermediate IMFs low compressibility Solid strong IMFs no compressibility Fusion melting solid liquid endothermic Vaporization liquid gas Endothermic Sublimation dry ice Solid gas Endothermic Freezing Liquid solid Exothermic Condensation Gas liquid Exothermic Deposition Gas solid exothermic Endothermic goes from a more ordered state to a less ordered state solid liquid gas Exothermic less ordered state to more ordered state Enthalpy of vaporization deltaHvap energy required to change 1 mol of a liquid to a gas at a certain temperature AS THE STRENGTH OF THE IMFs IN A SERIES OF LIQUID INCREASE THE ENTHALPY OF THE VAPORIZATION VALUES FOR THE LIQUIDS ALSO INCREASE The higher the equilibrium vapor pressure the more volatile the molecule the lower the boiling point VAPOR PRESSURE INCREASES WITH INCREASING TEMPERATURE When equilibrium is reached evaporation does not stop it s when the rate of evaporation and condensation are equal does all the liquid evaporate use PV nRT if p vp yes all liquid evaporates if p vp no all liquid does not evaporate Boiling point when VP equals exactly atmospheric pressure When vp exactly equals atmospheric pressure of 1 atm this is known as the normal boiling point When liquid boils the strength of IMFs are overcome THE HIGHER THE EQUILIBRIUM VP THE LOWER THE BP FOR A LIQUID AS IMF STRENGTH INCREASES The energy needed to vaporize the liquids deltaHvap will also increase The equilibrium VP decreases and consequently the liquid normal boiling point increases STONG IMF HIGH deltaHvap LOW VP HIGH BP Clausius Clapeyron equation relates the pressure temp and strength of IMFs Mainly used for calculating deltaHvap MAKE SURE TO USE KELVIN Surface Tension the toughness of a liquid skin Molecules at surface behave differently than those in the interior S T is the energy required to break through the surface Different molecules have different surface tensions Addition of soap to water changes the surface tension Capillary Action the forces between molecules and external devices When a glass tube with a small diameter is placed in water the water rises bc CapAction meniscus Water molecules are attracted to the glass surface by hydrogen bonding some water molecules adhere to the glass while others attract to other water molecules Lower vp higher bp Strength of IMFs is directly dependent on differing charges of interacting atoms the strength follows Coulombs Law which relates electric charge and distance Force is proportional to qA qB r 2 q being lowercase delta being partial charge Dipole Dipole in POLAR molecules Why does O2 a nonpolar molecule dissolve in H2O Dipole Induced Dipole Inducing a dipole form a seemingly nonpolar substance is called polarization THE GREATER THE MOLECULAR WEIGHT THE MORE POLARIZABLE STRONGER INDUCED DIPOLE IMF London Dispersion Forces LDF IN EVERYTHING Induced dipoles in 2 nonpolar molecules WEAKEST INTERACTION ONLY IMF PRESENT IN NONPOLAR MOLECULES As you go further down the periodic table the more polarizable molecules become Hydrogen Bonding polar with O N or F nothing else must be directly connected THE MORE HYDROGEN BONDING POTENTIAL THE HIGHER THE BP CHAPTER 13 Solvent the liquid doing to dissolving Solute the compound being dissolved Unsaturated Solution one that can dissolve more solute Saturated one that cannot dissolve more solute Supersaturated one that contains more dissolved solute at a given temperature very unstable Electronegativity low at bottom left corner of periodic table gets higher towards top right Cohesive Forces attractive forces that exist between molecules at the macroscopic level that affect the physical properties of a liquid Sometimes called bulk scale forces result of IMFs the molecular level interactions in a liquid Entropy the measure of disorder of a system also known as molecular randomness or freedom of molecular motion Increasing temperature increases entropy Enthalpy change the difference between the strength of a substances IMFs and the interaction between the solute and the species in the solution Increase in disorder Decrease in disorder more organized state Entropy change Entropy change Enthalpy Change Endo Favored at high temps Not favored at any temp Enthalpy Change Exo Favored at all temps Favored at low temps Flow chart in notes Miscible if 2 liquids mix Immiscible if 2 liquids do not mix Whether or not the liquids are miscible also depends on entropy and enthalpy LIKE DISSOLVES LIKE ie polar substances dissolve nonpolar substances The greater the dipole moment the stronger the IMF The greater the ions charge the stronger the IMF Boiling Point Elevation the addition of a solute will LOWER the VP but INCREASE the NBP The solutions which has a NBP will need to be heated to a higher temperature in order for the VPsoln to become equal to the atmospheric pressure Tbp Kbp mi Tbp change in BP of solvent Kbp BP elevation constant m molality of solution i Van t Hoff factor essentially 1 for nonelectrolyte solutions Freezing Point Depression solutes will lower the freezing point of the pure solvent Tfp Kfp mi Kfp freezing depression constant ALWAYS NEGATIVE Tf solution Tf solvent deltaTf KKfmi Osmotic Pressure Pi MRTi M molarity R 0 082057 ATM mol K T temp IN KELVIN I Van t Hoff Factor Hydration number increases with decreasing charge and decreasing radius smaller highly charged ions have very large hydration numbers Hydration enthalpy increases in magnitude as the ion charge increases and as radius decreases The smaller the hydration number the more favored the dissolution in terms of entropy low charge large radius Enthalpy of Solvation the energy associated with dissolving ions in a solvent when a solvent is water called enthalpy of hydration Can be endo or exo AS IONS BECOME LARGER THE INTERACTIONS BECOME WEAKER solvation is less exothermic with larger ions Solids dissolving in liquids temp is only factor Gases dissolved in liquids both pressure and temp are factors Dissolved Gasses and Henry s Law Sg KhPg Sg gas solubility Kh Henry s Law Constant Pg partial pressure Gas solubility is directly proportional to the pressure of the gas AS THE PRESSURE INCREASES THE SOLUBILITY ALSO INCREASES A GASSES SOLUBILITY DECREASES WITH INCREASING TEMPERATURE the solubility