CHEM 1212 Spring 2017 Chapter 11 Intermolecular Forces and the Liquid State Types of Intermolecular Interactions Forces Ion Ion Dipole Dipole Hydrogen Bonds London Dispersion Forces Induced Dipoles Hydrogen Bonding Hydrogen bonding is a special case of a dipoledipole interaction A hydrogen is bound to a VERY electronegative element N O or F and can then form a hydrogen bond with a neighboring N O or F Each of the bonds below has one element with a partial negative and one with a partial positive charge and are opposite in sign but equal in magnitude Which of these bonds has the largest partial charges on one of the atoms A B C D E N H C H H F B H H H Rank the following molecules from least to most polar ignore molecular weight differences A CH4 B CH3F C CH3Cl D CH3Br Determine the major IMF for each of these molecules and then rank those IMFs in order of increasing strength A CO2 B NH3 C CHCl3 D CCl4 Which of the following compounds exhibit hydrogen bonding in the pure liquid A B C D E F H2 O CH3OCH3 CH3CH2OH CH3NH2 N CH3 3 CH3CO2H A sodium ion would have the greatest interaction with which molecule A CH4 B CH3Cl C CH2Cl2 D CHCl3 E CCl4 Rank the compounds in order of increasing polarity A HCl B HBr C HI Rank the compounds in order of increasing boiling point A HCl B HBr C HI Why is the trend reversed A The trend for polarity was wrong B Boiling point is not dependent on the polarity of the molecules C London forces D Boiling point is more dependent on mass than intermolecular attractions E Boiling point is dependent on the interaction of strange attractors Rank the compounds in order of increasing polarity A HCl B HBr C HI Rank the compounds in order of increasing boiling point D HCl D 1 08 bp 85 C E HBr D 0 80 bp 66 C F HI D 0 42 bp 35 C HF D 1 91 bp 19 5 C Effect of IMF s and Boiling Point Intermolecular Forces and Physical Characteristics Most of the physical characteristics of solids and liquids are dependent upon the strength of the intermolecular forces keeping things together Heat of hydration Chapter 13 Vaporization Vapor Pressure Boiling Point Surface Tension Viscosity Vaporization Vaporization is the process where a particle in the liquid phase escapes in the gas phase Condensation is the reverse process As the temperature increases more particles will have enough energy to overcome the intermolecular forces holding them in the liquid phase and escape into the gas phase Vapor Pressure Suppose the liquid sample is in a closed container Some particles will have enough energy to escape from the liquid phase into the gas phase Some of the particles in the gas phase won t have enough energy to escape the attractive forces when they collide with the liquid surface and condense Vapor Pressure Definition The pressure exerted by a vapor in equilibrium with its solid or liquid at a given temperature in a closed system Vapor Pressure A liquid is said to boil when its vapor pressure is equal to the external pressure The normal boiling point is when the vapor pressure is equal to 1 atm or 760 torr Vapor Pressure As the intermolecular forces increase between particles the vapor pressure and the normal boiling point A B C D increases increases increases decreases decreases increases decreases decreases According to this plot increasing the temperature will the vapor pressure A increase B not change C decrease Vapor Pressure The equilibrium vapor pressure is the pressure exerted by the vapor in equilibrium with the liquid The vapor pressure of liquid bromine at room temperature is 168 torr Suppose that bromine is introduced drop by drop into a closed system containing air at 775 torr and room temperature The volume of liquid bromine is negligible compared to the volume of the system If the bromine is added until no more vaporizes and a few drops of liquid are present in the flask what would be the total pressure What would be the total pressure if the volume of this closed system were decreased to one half its original value at the same temperature Volume does not affect vapor pressure The liquid in a container is in equilibrium with the vapor When the volume is decreased some of the vapor in the container condenses to the liquid state Vapor Pressure Clausius Clapeyron Equation Estimate the vapor pressure at any temperature The vapor pressure of 1 propanol is 10 00 torr at 14 70 C Calculate the vapor pressure at 52 80 C Heat of vaporization of 1 propanol 47 2 kJ mol Gasoline is a mixture of hydrocarbons a major component of which is octane CH3CH2CH2CH2CH2CH2CH2CH3 Octane has a vapor pressure of 13 95 torr at 25 C and a vapor pressure of 144 78 torr at 75 C Calculate the heat of vaporization of octane in kJ mol Carbon tetrabromide is more volatile than carbon tetrachloride A True B False Carbon tetrabromide has a higher boiling point than carbon tetrachloride A True B False Carbon tetrabromide has weaker IMF s than carbon tetrachloride A True B False Carbon tetrabromide has a higher vapor pressure than carbon tetrachloride A True B False