CHAPTER 13 LIQUIDS AND SOLIDS 1 Kinetic Molecular Description of Liquids and Solids all ionic compounds are solid at room temperature have high melting points temperature intermolecular forces ordering all covalent compounds are gases or low melting point solids at room liquids and solids are highly incompressible liquids and solids are in condensed states very high degrees of strength of intermolecular forces strength increases with degree of solids liquids gases gases have almost no intermolecular forces miscible liquids are soluble in each other while immiscible liquids are cooling a liquid lowers its molecular kinetic energy which causes the not soluble in each other molecules to slow down 2 Intermolecular Attractions and Phase Changes generally speaking ionic bonding hydrogen bonding dipole dipole bonding London forces ion ion interactions governed by Coulomb s Law F q q d2 the higher and charges mean higher melting point and boiling point and lower water solubility this means that 2 2 is stronger than 1 1 also keep in mind that all ionic compounds are solids at room temperature ion dipole interactions remember this chart non polar covalent bond polar bond ionic bond EN 0 4 2 0 EN 2 0 EN 0 0 0 4 dipole dipole interactions occur between polar covalent compounds each element in a Lewis structure can be labeled as partial or partial negative occurs between a hydrogen and either 2 oxygens 2 nitrogens or 2 fluorines must look like one of the following O H O N H N or F H F hydrogen bonding intermolecular forces increase with increasing molar mass but all hydrogen bonds H with N O or F are still stronger regardless of molar mass London dispersion forces compounds only important in non polar compounds since these are the only forces present in non polar compounds a very temporary induced dipole the weakest bonds present in all 3 Viscosity The Liquid State viscocity within a liquid resistance to flow one measure of the forces of attraction honey and glycerin are viscous liquids i e they have high viscocities 4 5 6 Surface Tension The Liquid State surface tension a measure of the inward forces that must be overcome to expand the surface of a liquid molecules on the surface are attracted only toward the interior while those in the interior are attracted equally in all directions Capillary Action The Liquid State cohesive forces adhesive forces capillary action the forces that hold a liquid together the forces between a liquid and another surface water drawn up through the roots of plants capillary rise implies that adhesive forces cohesive forces capillary fall implies that cohesive forces adhesive forces Evaporation The Liquid State temperature dependent as temperature increases the amount of evaporation increases as well gas particles in an open beaker DO NOT have a vapor pressure of zero they have a vapor pressure equal to atmospheric pressure in a sealed container vapor pressure is created by gas particles colliding with each other and the sides of the container 7 Vapor Pressure The Liquid State due to intermolecular forces the amount of vapor and the boiling point both increase as you make your way DOWN the following chart vapor pressures for three common liquids compound name type of bonds diethyl ether CH3OCH3 methanol CH2CH2OH water H2O dipole dipole hydrogen bonding hydrogen bonding 0 oC 25 oC 50 oC normal boiling point 185 torr 470 torr 1325 torr 36 oC 29 7 torr 122 torr 404 torr 78 oC 4 6 torr 23 8 torr 92 5 torr 100 oC note that the C O bond is weaker than the O H bond because of the incredible strength of hydrogen bonds 8 Boiling Points and Distillation The Liquid State boiling point equals the applied usually atmospheric pressure the temperature at which the vapor pressure of a liquid in the chart below HF has a much higher boiling point in relation to its molecular weight than HCl HBr and HI because HF has hydrogen bonds while HCl HBr and HI are all dipole dipole compound HF HCl HBr HI molecular weight 20 amu 37 amu 81 amu 128 amu boiling point 19 5 oC 85 0 oC 67 0 oC 34 0 oC so hydrogen bonding liquids have abnormally high boiling points normal boiling point the temperature at which the vapor pressure of a liquid equals 760 torr 1 00 atm into its components on the basis of differences in boiling points of the components the process by which a mixture or solution is separated distillation see drawing in lecture outline 9 Heat Transfer Involving Liquids The Liquid State specific heat J g oC or Cal g oC the amount of heat required to raise the temperature of 1 00 g of a substance 1 oC with no change in state Q m C T see lecture outline to see when to use each equation note that T is an absolute value meaning it is ALWAYS positive molar heat capacity temperature of 1 00 mol of a substance 1 oC with no change in state the amount of heat required to raise the Q mol J mol oC T heat of vaporization J g the amount of heat that must be absorbed to convert 1 00 g of a liquid at its boiling point to a gas with no change in temperature J endothermic adding heat energy flows into the system heat of condensation amount of heat that must be removed to liquefy 1 00 g of a gas as its condensation boiling point with no change in temperature J g the reverse of the heat of vaporization the J exothermic removing heat energy flows out of the system molar heat of vaporization H vap J mol the amount of heat that must be absorbed to convert 1 00 mol of a liquid at its boiling point to a gas with no change in temperature of vaporization H con J mol the reverse of the molar heat molar heat of condensation 10 Melting Point The Solid State normal melting point the temperature at which the solid melts liquid and solid are in equilibrium at exactly 1 00 atm of pressure this increases as the strength of the intermolecular attractions increases 11 Heat Transfer Involving Solids The Solid State heat of fusion gram of a solid at its melting point at constant temperature note that melting solid liquid is endothermic H fusion J g the amount of heat required to melt 1 00 heat of crystallization H crystal J g solidification the reverse of the heat of fusion the amount of heat liberated by the crystallization of 1 00 g of liquid at its freezing point equal to the amount of heat required to melt 1 00 g of the solid at its melting point note that freezing liquid solid is exothermic molar heat of fusion melt 1 00 mol of a substance at its melting point H fusion J mol the amount of heat required to note that