12 2 Properties of Liquids 13 1 Crystal Lattices and Unit Cells Physical Characteristics of Liquids Heat of vaporization Vapor pressure Boiling point vapor pressure atmospheric pressure o Faster version of evaporation Surface tension o Ex water bugs on surface of pond Capillary action o Water molecules Viscosity o Ex pouring out syrup Clicker Match the heat of vaporization with the compound 1 2 3 4 C2H6 A 14 7 kJ mol H2O B 8 2 kJ mol SO2 C 24 9 kJ mol CH4 D 40 7 kJ mol A D C B Methane London dispersion forces Ethane London dispersion forces o Longer chain bigger molecule o Cloud distortions temporary dipoles more likely o London dispersion forces increase with the size of the molecules Sulfur dioxide dipole dipole o Draw Lewis structure is the molecule polar o Lone pair on S so it is bent and polar Water dipole dipole o Has H bonding special case N2 to O2 not quite mass it s the size O2 has stronger intermolecular forces N2 has triple bonds and one lone pair on each N O2 has double bonds and two lone pairs on each O More fluff around O2 molecule Clicker 200 mL of water are added to two closed vessels One has a volume of 1L A and the other has a volume of 5L B If both vessels are at the same temperature Which vessel will have the higher vapor pressure A1L B5L C same Vapor pressure will be the same for the two vessels Which vessel will have more water molecules in the vapor phase A1L B5L C same Both reach same vapor pressure which means more water molecules go into gas phase in the 5 L than the 1 L Vapor pressure is constant between the two bottles Example A lower intermolecular force lower heat of vaporization B higher intermolecular force higher heat of vaporization A has higher vapor pressure easier for molecules to get into gas phase B has lower vapor pressure harder for molecules to get into gas phase Clicker Is it possible for both vessels to have the same number of molecules in the vapor phase A yes B no Clicker The normal boiling point is defined as A the temperature at which a substance usually boils B the temperature at which the vapor pressure of the liquid equals the external pressure C the temperature at which the vapor pressure is equal to one atm D the temperature at which the vapor pressure equals atmospheric pressure D incorrect normal boiling point is not the same everywhere A usually incorrect C 1 atm is constant same no matter where you go Raise temperature raising vapor pressure Get to point where it stops acting normal London dispersion forces increasing boiling point increases CH4 SiH4 GeH4 SnH4 Dipole dipole H bond NH3 HF H2O Critical Point Above some high temp and pressure substances will begin to behave as a supercritical fluid A supercritical fluid has the physical characteristics of a gas but the density resembles that of a liquid o gas but has density more related to a liquid o has characteristics of both gas and liquid Ex decaf coffee using CO2 in a supercritical state o Can move supercritical fluid into another reservoir reduce temperature change pressure goes back to gas phase o Doesn t just extract caffeine also extracts other thing changes taste Earth have to be in closed container due to normal pressure being 1 atm Other planets that environment is different making supercritical fluids Most molecules and compounds have supercritical points but not on Earth o Maybe on suns stars or other planets Capillary Action Related to intermolecular attractions between the substance the walls of the capillary Where there is a strong interaction the liquid will climb the walls Where there is little to no interaction the surface tension will cause the surface to bubble o Ex mercury thermometer mercury bubbles up on surface surface tension o Ex alcohol or water thermometer water alcohol concaves down on surface capillary action