CHEM 1212 1st Edition Lecture 2Outline of Last Lecture I. States of Matter and Intermolecular ForcesII. Interactions between Ions and Molecules with a Permanent DipoleIII. Interactions between Molecules with a Dipolea. Dipole-Dipole Forcesb. Hydrogen Bondingc. Hydrogen Bonding and the Unusual Properties of WaterIV. Intermolecular Forces Involving Nonpolar Moleculesa. Dipole-Induced Dipole Forcesb. London Dispersion Forces: Induced Dipole-Induced DipoleV. A Summary of van der Waals Intermolecular ForcesOutline of Current Lecture I. Properties of Liquidsa. Vaporization and Condensationb. Vapor Pressurec. Vapor Pressure, Enthalpy of Vaporization, and the Clausius-Clapeyron EquationII. Crystal Lattices and Unit CellsCurrent LectureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.I. Properties of LiquidsVaporization and Condensationa. Vaporization (Evaporation) – the process in which a substance in the liquid state becomes a gasb. As molecules gain kinetic energy through raising temp they are able to break the interactions with the neighboring molecules and escape the liquid as a gasc. Vaporization is an endothermic process because it requires the input of energy to overcome the intermolecular forcesd. The energy required to vaporize a sample is often given as the standard molar enthalpy of vaporizationi. Liquid -----(vaporization/energy absorbed)-- gase. As gas molecules lose their kinetic energy, they are then able to reenter the liquid phase (called condensation) – think of it as the gas condensing back into a liquidf. Condensation is the reverse process of vaporization, it is exothermic because energy is transferred to the surroundingsg. The enthalpy change for condensation is equal but opposite in sign to the enthalpy of vaporizationi. Ex: The enthalpy of vaporization for 1 mol of water at 100 degrees Celsius is +40.7 kJ1. The enthalpy of condensation of 1 mol of water vapor at 100 degrees Celsius is -40.7 kJii. Vapor------ (condensation/energy released)--liquidh. The boiling points of nonpolar liquids increase with increasing molecular massi. In the heavier hydrogen halide (H and Cl, Br, or I) the boiling points and enthalpies increase with increasing massi. In these three molecules, London forces and dipole-dipole forces are responsiblefor the intermolecular attractionsj. Among the hydrogen halides, HF, is the exceptioni. HF has a much higher boiling point and enthalpy of vaporization due to the extensive hydrogen bonding in the moleculek. The process of evaporation is what is happening when we work out; our energy heats upthe water molecules in our body and they turn to vapor (sweat)l. Rain is just the condensation of water vapors in the skyVapor Pressurem. Water in an open container with eventually evaporate completely because the escaping water vapor molecule will leave the container n. Water in a closed container will remain all in the container, because the water vapor molecules can not escape and some will re-condense to again form liquidi. Eventually the masses of liquid and vapor in the container will remain constant (meaning that they are at a dynamic equilibrium)ii. At equilibrium, the rate at which molecules change from liquid to vapor is equivalent to the rate at which they change from vapor to liquid; this results no net change in the masses of the two phaseso. Equilibrium Vapor pressure (aka vapor pressure)i. The vapor pressure can be measured once the two phases reach the liquid-vapor equilibriumii. Vapor pressure is defined as the pressure exerted by the vapor in equilibrium with the liquid phase (the tendency of molecules to escape from liquid to vapor phase at a given temperature)Vapor Pressure, Enthalpy of Vaporization, and the Clausius-Clapeyron Equationp. Clausius-Clapeyron equation – provides a method for obtaining values of the enthalpy of vaporizationi. ln P = - (enthalpy of vaporization/RT) + Cln P = vapor pressureR = ideal gas constant (8.314472 J/K x mol)T = tempC = constant characteristic of liquid in questionq. Another way to calculate enthalpy of vaporization can be used if you have the vapor pressure of a liquid at two different temperaturesln P2/P1 = (-enthalpy of vaporization/R)[1/T2 – 1/T1]Boiling Pointr. Boiling point is the temperature at which a liquids vapor pressure is equal to the externalpressure, allowing bubbles of water vapor to float to the surfaces. Normal Boiling Point – the temperature at which that external pressure is 760 mm Hgi. Normal boiling point of water is 100 degrees Celsius Critical Temperature and Pressuret. Critical point – when a high enough temperature is reached and the interface between the liquid and the vapor disappears i. Tc – the temperature at which critical point is reachedii. Pc – the pressure at which the critical point is reachedu. Supercritical fluid – (a fluid that exists under these conditions) it is like a gas under such high pressure that its density resembles that of a liquid, but its viscosity remains close to that of a gasi. The molecules are pushed closely together like they are in a liquid, but each molecule has just enough energy to overcome the intermolecular forcesSurface Tension, Capillary Action, and Viscosityv. Unlike molecules in the middle of a liquid (which interact with other molecules all around them), molecules on the surface of a liquid only interact with molecules at or below the surfacei. Leads to an inward force of attraction, contracting the surface molecules and making them behave as a sort of skin for the liquidw. Surface Tension – the energy required to break through the surface or to disrupt a liquid drop i. This is what causes water droplets to be contained in little spheresx. Capillary action – demonstrated by a glass tube in water, water will rise inside the tube just as water would climb up a piece of paper if it was placed in wateri. Adhesive forces create an attracting between the polar water molecules and the polar molecules on the surface of the glass tubeii. Cohesive forces between the water and the glass cause the water level inside the tube to rise until the attractive forces are balanced by the force of gravity pulling down on the water column 1. This leads to the concave meniscus seen with water in a test tubeiii. There are rare exceptions such as mercury where the surface tension is much stronger than the adhesive forces