Intermolecular Forces Chapter 11 Intermolecular Forces, Liquids, and Solids John D. Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc. Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten

Intermolecular Forces States of Matter The fundamental difference between states of matter is the distance between particles.

Intermolecular Forces States of Matter Because in the solid and liquid states particles are closer together, we refer to them as condensed phases.

Intermolecular Forces The States of Matter The state a substance is in at a particular temperature and pressure depends on two antagonistic entities:  The kinetic energy of the particles  The strength of the attractions between the particles

Intermolecular Forces a. gas 1.No comparison can be made between kinetic and attraction energy without temperature information. 2.The average kinetic energy is greater than the energy of attraction. 3.The average kinetic energy is equal to the energy of attraction. 4.The average kinetic energy is less than the energy of attraction.

Intermolecular Forces a. gas 1.No comparison can be made between kinetic and attraction energy without temperature information. 2.The average kinetic energy is greater than the energy of attraction. 3.The average kinetic energy is equal to the energy of attraction. 4.The average kinetic energy is less than the energy of attraction.

Intermolecular Forces b. solid 1.No comparison can be made between kinetic and attraction energy without temperature information. 2.The average kinetic energy is equal to the energy of attraction. 3.The average kinetic energy is greater than the energy of attraction. 4.The average kinetic energy is less than the energy of attraction.

Intermolecular Forces b. solid 1.No comparison can be made between kinetic and attraction energy without temperature information. 2.The average kinetic energy is equal to the energy of attraction. 3.The average kinetic energy is greater than the energy of attraction. 4.The average kinetic energy is less than the energy of attraction.

Intermolecular Forces Intermolecular Forces Affect Many Physical Properties The strength of the attractions between particles can greatly affect the properties of a substance or solution.

Intermolecular Forces Viscosity Resistance of a liquid to flow is called viscosity. It is related to the ease with which molecules can move past each other. Viscosity increases with stronger intermolecular forces and decreases with higher temperature.

Intermolecular Forces Surface Tension Surface tension results from the net inward force experienced by the molecules on the surface of a liquid.

Intermolecular Forces Cohesive forces bind similar molecules to one another, like hydrogen bonding in water Intermolecular forces that bind a substance to a surface are adhesive forces

Intermolecular Forces Adhesive forces between water and glass are greater than cohesive forces and water adheres to it, causing a U- shaped meniscus With mercury the cohesive forces are stronger Adhesive forces are responsible for capillary action

Intermolecular Forces a. 1.Both viscosity and surface tension decrease with increasing temperature. 2.Viscosity increases with increasing temperature while surface tension decreases. 3.Viscosity decreases with increasing temperature while surface tension increases. 4.Both viscosity and surface tension increase with increasing temperature.

Intermolecular Forces a. 1.Both viscosity and surface tension decrease with increasing temperature. 2.Viscosity increases with increasing temperature while surface tension decreases. 3.Viscosity decreases with increasing temperature while surface tension increases. 4.Both viscosity and surface tension increase with increasing temperature.

Intermolecular Forces b. 1.Viscosity increases as intermolecular forces increase while surface tension decreases. 2.Viscosity decreases as intermolecular forces increase while surface tension increases. 3.Both viscosity and surface tension increase as intermolecular forces increase. 4.Both viscosity and surface tension decrease as intermolecular forces increase.

Intermolecular Forces b. 1.Viscosity increases as intermolecular forces increase while surface tension decreases. 2.Viscosity decreases as intermolecular forces increase while surface tension increases. 3.Both viscosity and surface tension increase as intermolecular forces increase. 4.Both viscosity and surface tension decrease as intermolecular forces increase.

Intermolecular Forces 1.The polarity of the substance is necessary to determine which force is most important. 2.Viscosity and surface tension are not related to adhesive and cohesive forces. 3.adhesive forces 4.cohesive forces

Intermolecular Forces 1.The polarity of the substance is necessary to determine which force is most important. 2.Viscosity and surface tension are not related to adhesive and cohesive forces. 3.adhesive forces 4.cohesive forces

Intermolecular Forces Phase Changes Phase changes (changes from solid, liquid or gas) are accompanied by changes of energy in the system Energy increases will increase kinetic energy, increasing movement Enough energy, solids will melt and liquids become gases

Intermolecular Forces Phase Changes

Intermolecular Forces Energy Changes Associated with Changes of State Heat of Fusion: Energy required to change a solid at its melting point to a liquid.

Intermolecular Forces Energy Changes Associated with Changes of State Heat of Vaporization: Energy required to change a liquid at its boiling point to a gas. Notice  H vap requires more energy There is a  H sub for sublimation =  H vap +  H fus

Intermolecular Forces Changes of state video clip

Intermolecular Forces Heat solid  melt  boil  heat gas is an endothermic process Cool gas  condense  cool liquid  freeze is exothermic

Intermolecular Forces 1.evaporation, endothermic 2.melting (or fusion), endothermic 3.sublimation, endothermic 4.melting (or fusion), exothermic

Intermolecular Forces 1.evaporation, endothermic 2.melting (or fusion), endothermic 3.sublimation, endothermic 4.melting (or fusion), exothermic

Intermolecular Forces Which one of the following phase changes is an exothermic process? 1.Sublimation 2.Vaporization 3.Condensation 4.Melting

Intermolecular Forces Correct Answer: All the other phase-change processes listed are endothermic. 1.Sublimation 2.Vaporization 3.Condensation 4.Melting

Intermolecular Forces Energy Changes Associated with Changes of State The heat added to the system at the melting and boiling points goes into pulling the molecules farther apart from each other. The temperature of the substance does not rise during the phase change. A heating curve

Intermolecular Forces Practice Exercise Calculate the enthalpy change upon converting 1.00 mol of ice at -25C to water vapor (steam) at 125C under a constant pressure of 1 atm. The specific heats of ice, water and steam are 2.09 J/g-K, 4.18 J/g-K, and 1.84 J/g-K, respectively. For water,  H fus = 6.01 kJ/mol and  H vap = kJ/mol

Intermolecular Forces Practice Exercise What is the enthalpy change during the process in which g of water at 50.0C is cooled to ice at -30.0C? The specific heats of ice, water and steam are 2.09 J/g-K, 4.18 J/g-K, and 1.84 J/g-K, respectively. For water,  H fus = 6.01 kJ/mol and  H vap = kJ/mol

Intermolecular Forces Vapor Pressure At any temperature, some molecules in a liquid have enough energy to escape. As the temperature rises, the fraction of molecules that have enough energy to escape increases.

Intermolecular Forces Vapor Pressure As more molecules escape the liquid, the pressure they exert increases.

Intermolecular Forces Vapor Pressure The liquid and vapor reach a state of dynamic equilibrium: liquid molecules evaporate and vapor molecules condense at the same rate.

Intermolecular Forces Vapor Pressure The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure. The normal boiling point is the temperature at which its vapor pressure is 760 torr.

Intermolecular Forces Vapor pressure video

Intermolecular Forces Phase Diagrams Phase diagrams display the state of a substance at various pressures and temperatures and the places where equilibria exist between phases.

Intermolecular Forces Phase Diagrams The AB line is the liquid-vapor interface. It starts at the triple point (A), the point at which all three states are in equilibrium.

Intermolecular Forces Phase Diagrams It ends at the critical point (B); above this critical temperature and critical pressure the liquid and vapor are indistinguishable from each other.

Intermolecular Forces Phase Diagrams Each point along this line is the boiling point of the substance at that pressure.

Intermolecular Forces Phase Diagrams The AD line is the interface between liquid and solid. The melting point at each pressure can be found along this line.

Intermolecular Forces Phase Diagrams Below A the substance cannot exist in the liquid state. Along the AC line the solid and gas phases are in equilibrium; the sublimation point at each pressure is along this line.

Intermolecular Forces Phase diagram video

Intermolecular Forces Phase Diagram of Water Note the high critical temperature and critical pressure:  These are due to the strong van der Waals forces between water molecules.

Intermolecular Forces Phase Diagram of Water The slope of the solid– liquid line is negative.  This means that as the pressure is increased at a temperature just below the melting point, water goes from a solid to a liquid.

Intermolecular Forces Phase Diagram of Carbon Dioxide Carbon dioxide cannot exist in the liquid state at pressures below 5.11 atm; CO 2 sublimes at normal pressures.

Intermolecular Forces Phase Diagram of Carbon Dioxide The low critical temperature and critical pressure for CO 2 make supercritical CO 2 a good solvent for extracting nonpolar substances (such as caffeine).

Intermolecular Forces 1.There is no trend in the slope of the solid/liquid melting point line. 2.The solid/liquid melting point line usually has a positive slope (i.e., slopes to right). 3.The solid/liquid melting point line is straight up and down, parallel to the y-axis. 4.The solid/liquid melting point line usually has a negative slope (i.e., slopes to left).

Intermolecular Forces 1.There is no trend in the slope of the solid/liquid melting point line. 2.The solid/liquid melting point line usually has a positive slope (i.e., slopes to right). 3.The solid/liquid melting point line is straight up and down, parallel to the y-axis. 4.The solid/liquid melting point line usually has a negative slope (i.e., slopes to left).

Intermolecular Forces Temperature Pressure A D C B In the unlabeled phase diagram below, the line segment from A to B separates which two phases? 1.Gas-liquid 2.Liquid-solid 3.Solid-gas

Intermolecular Forces Correct Answer: 1.Gas-liquid 2.Liquid-solid 3.Solid-gas Temperature Pressure A D C B

Intermolecular Forces Which statement is true? Boiling point ~120°C Boiling point ~95°C Boiling point ~75°C Melting point ~95°C Melting point ~75°C Vapor Pressure (mm Hg) Temperature ( ° C) 0

Intermolecular Forces Which statement is true? Boiling point ~120°C Boiling point ~95°C Boiling point ~75°C Melting point ~95°C Melting point ~75°C Vapor Pressure (mm Hg) Temperature ( ° C) 0