Dr. Pérez CHM1046C - Chapter 11a pg 1 of 12 (1) CH. 11 Intermolecular Forces, Liquids and Solids Objectives Determine intermolecular forces of covalent compounds and atoms Predict properties of liquids Understand/calculate Vapor Pressure Understand boiling and freezing points Understand/calculate heat involved in phase changes Understand Phase Diagrams, recognize components Know types of crystalline Solids Predict properties of solids (Note: We will skip sections 11.10, 11.11, 11.13) (2) GOAL (11.2): Understand and determine the type of intermolecular force present (3) Boiling Points of Selected Compounds Alkanes and Ketones M.M. (g/mol) Bp ( o C) Butane CH3CH2CH2CH3 58.1-0.5 Pentane CH3CH2CH2CH2CH3 72.2 36.1 Hexane CH3CH2CH2CH2CH2CH3 86.2 69 Acetone CH3CCH3 2-pentanone This number corresponds to the slide number on the top right corner of PowerPoint O O CH3CH2CH2CCH3 2-hexanone O 58.1 56.2 86.1 102 100 128 CH3CH2CH2CH2CCH3 Compare the boiling point of two compounds of roughly the same molar mass. Propose a hypothesis that explains the cause of the observations.
Dr. Pérez CHM1046C - Chapter 11a pg 2 of 12 (4) Dipole-Dipole Forces Occurs when molecules interact. Stronger Strength of Attraction Stronger Strength of Attraction Polarity Distance Draw a picture that illustrates this force: (5) London Dispersion Forces Due to motion of Causes dipole: Polarizability Present in all uncombined atoms, polar and non-polar molecules
Dr. Pérez CHM1046C - Chapter 11a pg 3 of 12 (6) STRENGTH OF London Dispersion Forces DEPENDS ON: (1) Molecules: The greater the number of places on molecule (chain), the the strength of attraction to other molecules of the same type. Long, skinny molecules tend to have dispersion forces than short, fat ones. (2) Uncombined atoms: The more, the greater the chances for distortion of the electron cloud (polarizability), and thus the the strength of attraction to other molecules of the same type. (7) Which of the following two hydrocarbons would have the greater boiling point? A. Propane (C3H8) B. Hexane (C6H14) (8) Read the answers you recorded on slide 4. Answer and complete table. Alkanes and Ketones M.M. (g/mol) Bp ( o C) Type of Covalent Compound Intermolecular Force Butane CH3CH2CH2CH3 58.1-0.5 Pentane CH3CH2CH2CH2CH3 72.2 36.1 Hexane CH3CH2CH2CH2CH2CH3 86.2 69 Acetone O 58.1 56.2 CH3CCH3 2-pentanone O 86.1 102 CH3CH2CH2CCH3 2-hexanone O 100 128 CH3CH2CH2CH2CCH3
Dr. Pérez CHM1046C - Chapter 11a pg 4 of 12 (9) More Boiling Points Alcohols M.M. (g/mol) Bp ( o C) 1-propanol CH3CH2CH2OH 60.1 97.4 1-butanol CH3CH2CH2CH2OH 74.1 117 1-pentanol CH3CH2CH2CH2CH2OH 86.2 137 1-hexanol CH3CH2CH2CH2CH2CH2OH 102 158 The data from slide 8 was plotted in the graph below. Data for alkanes and ketones from slide 9 are graphed below. Draw a smooth line to show their trends. Plot the alcohols on the graph. Add a smooth trend line. Propose an explanation for the observations. Boiling Points of Selected Compounds 160 Boiling Point ( o C) 140 120 100 80 60 40 20 Alkanes Ketones Alcohols 0-20 0 20 40 60 80 100 120 Molar Mass (g/mol)
Dr. Pérez CHM1046C - Chapter 11a pg 5 of 12 (10) Hydrogen Bonding A dipole-dipole force due to The small size of the elements enables the + to closely approach the - creating a very strong dipole. The relatively large difference leads to especially polar bonds. The H of an N H, O H, or F H group is strongly attracted to the pair electrons of an O, N, or F of molecule (11) The Boiling Points of the Covalent Hydrides of Elements e Hall, 2001. (12) Ion-Dipole Forces Present in of. The strength of these forces are what make it possible for substances to dissolve in solvents. Stronger Strength of Attraction Stronger Strength of Attraction Polarity Ion Size
Dr. Pérez CHM1046C - Chapter 11a pg 6 of 12 (13) Forces Intramolecular: Attractions between atoms a molecule (= ) Determines properties Approximate energy 100 1000 kj/mol Intermolecular: Attractions that occur particles (atoms or molecules). Determines properties Approximate energy 1 50 kj/mol Type Strength Occurs between Ion Dipole Hydrogen Bonding Dipole-Dipole London Dispersion Moderate:10-50 kj/mol Moderate:10-40 kj/mol Weak 3-4 kj/mol Weak 1-10 kj/mol Collectively referred to as van der Waals forces. Present ONLY in Compounds (14) Practice: What type of intermolecular attractive forces are present in the following substances? Substance Structure Ion- Dipole- Hydrogen London Dipole? Dipole? Bonding? Forces? NH3 PH3 BH3 KBr(aq)
Dr. Pérez CHM1046C - Chapter 11a pg 7 of 12 (15) Quiz Substance Structure Ion- Dipole? Dipole- Dipole? Hydrogen Bonding? London Forces? H2S Kr SF4 Assignment: EOCE (end-of-chapter excercises): 11.49, 11.51 (16) GOALS (11.4) Define the following properties of liquids, and relate these properties to the intermolecular forces involved: Surface Tension Capillary Action Viscosity Phase changes Vapor Pressure (17) 11.4 PROPERTIES OF LIQUIDS: VISCOSITY A measure of the liquid s to flow. intermolecular force viscosity The longer the molecule the viscosity. temperature viscosity. The more spherical the molecular shape, the viscosity
Dr. Pérez CHM1046C - Chapter 11a pg 8 of 12 (18) PROPERTIES OF LIQUIDS: SURFACE TENSION Resistance of a liquid to increase in. Caused by the net force experienced by the molecules on the surface of a liquid. Shape with smallest surface area - intermolecular force surface tension temperature surface tension (19) PROPERTIES OF LIQUIDS: CAPILLARY ACTION The rising of a liquid in a narrow tube. Exercise: Draw graduated cylinder and meniscus for: Concave: CF AF Convex: CF AF Two forces involved: Cohesive forces (CF) hold the liquid molecules together. Adhesive forces (AF) attract the outer liquid molecules to the tube s surface. (20) 11.2 Changes in Physical State Tro, Chemistry, 3 rd ed. Pearson, 2014.
Dr. Pérez CHM1046C - Chapter 11a pg 9 of 12 (21) Some Phase Changes Boiling point (Tb) The at which the liquid s equals the. Normal boiling point boils at. atmospheric pressure Tb Intermolecular force Tb Freezing point - the at which a pure changes to a. Melting point - the at which a becomes a. identical to the freezing point atmospheric pressure Tf /Tm Intermolecular force Tf /Tm Ex. (23) PROPERTIES OF LIQUIDS: EVAPORATION Molecules in the liquid are constantly in. The average kinetic energy is proportional to the temperature. Fig. 11.4 Tro, Chemistry, 3 rd ed. Pearson, 2014 Vaporization process by which energy can overcome intermolecular forces producing phase change from liquid to gas Rate of evaporation is dependent on: The strengths of intermolecular force : intermolecular force rate The temperature: T Ek rate The surface area: surface area rate Volatile -
Dr. Pérez CHM1046C - Chapter 11a pg 10 of 12 (24) 1. Greater intermolecular force: A. NF3 B. PF3 (25) 2. Highest boiling point: A. CBr4 B. CF4 C. CI4 (26) 3. Lowest freezing point: A. NaBr B. N2 C. HCl (27) 4. Lowest vapor pressure at 25 o C A. CH3CH2OCH2CH3 B. CH3CH2CH2CH2OH C. CH3CH2CH2CH3 (28) 5.Greatest a viscosity: A. H2S B. H2O2 C. SiH4 (29) 6. Lower melting point: A. Left B. Right Assignment: EOCE Assignment: EOCE 11.53, 11.55, 11.57, 11.59, 11.61, 11.63, 11.65, 11.67, 11.69
Dr. Pérez CHM1046C - Chapter 11a pg 11 of 12 (30) GOAL: Calculate the heat change involved over a range of temperatures (section 11.7) (31) Energy Changes Associated with Changes of State Fig. 11.36: Heating curve for water. Tro, Chemistry, 3 rd ed. Pearson, 2014 (32) Heat of Phase Transition Heat of vaporization ( H o vap)- The amount of energy required to vaporize 1 mole of a substance (measured at 1 atm & the temperature of the change). Heat of fusion ( H o fus)- The amount of energy required to melt 1 mole of a substance (measured at 1 atm & the temperature of the change). Heat of sublimation ( H o sub)- The amount of energy required to sublime 1 mole of a substance (measured at 1 atm & the temperature of the change). (33) Quantitative Aspects of Phase Changes The total enthalpy change is the of the changes of the individual steps. - Calculating the enthalpy during the change in temperature within a phase (Chapter 6): - Calculating the enthalpy of a phase change: Note: You need to assign the Hphase change sign.
Dr. Pérez CHM1046C - Chapter 11a pg 12 of 12 (34) Problem 1 Calculate Energy How much energy does it take to convert 1.000 kg of steam at 300.0 o C ice at 32.0 o C? The specific heat capacities of H2O are: ice, 2.1 J/g o C liquid, 4.2 J/g o C steam, 2.0 J/g o C For H2O, Δ Hvap = 40.67 kj/mol and Δ Hfus = 6.01 kj/mol. Assignment: 11.79, 11.83, 11.127, 11.154 Print Ch 11b Outline from Blackboard. Before next class: Watch Videos for Chapter 11 found in Blackboard in the Class Videos tab on the left toolbar.