Chapter 14. Liquids and Solids

Chapter 14 Liquids and Solids

Section 14.1 Water and Its Phase Changes Reviewing What We Know Gases Low density Highly compressible Fill container Solids High density Slightly compressible Rigid (keeps its shape) Copyright Cengage Learning. All rights reserved 2

Section 14.1 Water and Its Phase Changes Heating/Cooling Curve Normal boiling point: at 1 atm = 100 C Normal freezing point: at 1 atm = 0 C Density Liquid water = 1.00 g/ml Ice = 0.917 g/ml Copyright Cengage Learning. All rights reserved 4

Section 14.1 Water and Its Phase Changes Concept Check During the process of melting ice by adding heat, the temperature of the ice/liquid water slurry a) stays constant. b) increases. c) decreases. d) cannot be predicted. Copyright Cengage Learning. All rights reserved 5

Section 14.2 Energy Requirements for the Changes of State Phase Changes When a substance changes from solid to liquid to gas, the molecules remain intact. The changes in state are due to changes in the forces among molecules rather than in those within the molecules. Copyright Cengage Learning. All rights reserved 7

Section 14.2 Energy Requirements for the Changes of State Phase Changes Solid to Liquid As energy is added, the motions of the molecules increase, and they eventually achieve the greater movement and disorder characteristic of a liquid. Liquid to Gas As more energy is added, the gaseous state is eventually reached, with the individual molecules far apart and interacting relatively little. Copyright Cengage Learning. All rights reserved 8

Section 14.2 Energy Requirements for the Changes of State Intramolecular Forces Within the molecule. Molecules are formed by sharing electrons between the atoms. Hold the atoms of a molecule together. Copyright Cengage Learning. All rights reserved 9

Section 14.2 Energy Requirements for the Changes of State Intermolecular Forces Forces that occur between molecules. Intramolecular forces are stronger than intermolecular forces. Copyright Cengage Learning. All rights reserved 10

Section 14.2 Energy Requirements for the Changes of State Molar heat of fusion energy required to melt 1 mole of a substance. Molar heat of vaporization energy required to change 1 mole of a liquid to its vapor. Copyright Cengage Learning. All rights reserved 11

Section 14.2 Energy Requirements for the Changes of State Concept Check Which are stronger, intramolecular forces or intermolecular forces? How do you know? Copyright Cengage Learning. All rights reserved 12

Section 14.2 Energy Requirements for the Changes of State Concept Check Which would you predict should be larger for a given substance: H vap or H fus? Explain why. Copyright Cengage Learning. All rights reserved 13

Section 14.2 Energy Requirements for the Changes of State Concept Check The unusually high value of the molar heat of vaporization of water (40.6 kj/mole) is an important factor in moderating the temperature of the earth s surface, and results in an enormous transfer of energy to the atmosphere as liquid water evaporates as part of the hydrologic cycle. Calculate the amount of heat in kj needed to evaporate 10.5 kg of liquid water at 100. o C. a) 4.27 10 5 kj b) 3.15 10 4 kj c) 2.37 10 4 kj d) 1.18 10 3 kj 1000 g 1 mol H O 40.6 kj 1 kg 18.016 g H O mol 2 4 10.5 kg H O = 2.37 10 kj 2 2 Copyright Cengage Learning. All rights reserved 14

Section 14.3 Intermolecular Forces Dipole-Dipole Forces Dipole moment molecules with polar bonds often behave in an electric field as if they had a center of positive charge and a center of negative charge. Molecules with dipole moments can attract each other electrostatically. They line up so that the positive and negative ends are close to each other. Only about 1% as strong as covalent or ionic bonds. Copyright Cengage Learning. All rights reserved 17

Section 14.3 Intermolecular Forces Hydrogen Bonding Strong dipole-dipole forces. Hydrogen is bound to a highly electronegative atom nitrogen, oxygen, or fluorine. Copyright Cengage Learning. All rights reserved 18

Section 14.3 Intermolecular Forces London Dispersion Forces Instantaneous dipole that occurs temporarily in a given atom induces a similar dipole in a neighboring atom. Significant in large atoms/molecules. Occurs in all molecules, including nonpolar ones. Copyright Cengage Learning. All rights reserved 21

Section 14.3 Intermolecular Forces Melting and Boiling Points In general, the stronger the intermolecular forces, the higher the melting and boiling points. Copyright Cengage Learning. All rights reserved 24

Section 14.3 Intermolecular Forces Concept Check Draw two Lewis structures for the formula C 2 H 6 O and compare the boiling points of the two molecules. H H H H H C C O H H C O C H H H H H Copyright Cengage Learning. All rights reserved 26

Section 14.3 Intermolecular Forces Concept Check Consider the following compounds: NH 3 CH 4 H 2 How many of the compounds above exhibit London dispersion forces? a) 0 b) 1 c) 2 d) 3 Copyright Cengage Learning. All rights reserved 28

Section 14.4 Evaporation and Vapor Pressure Vaporization or Evaporation Molecules of a liquid can escape the liquid s surface and form a gas. Endothermic process requires energy to overcome the relatively strong intermolecular forces in the liquid. Copyright Cengage Learning. All rights reserved 29

Section 14.4 Evaporation and Vapor Pressure Vapor Pressure Amount of liquid first decreases then becomes constant. Condensation - process by which vapor molecules convert to a liquid. When no further change is visible the opposing processes balance each other equilibrium Copyright Cengage Learning. All rights reserved 30

Section 14.4 Evaporation and Vapor Pressure Vapor Pressure Pressure of the vapor present at equilibrium. The system is at equilibrium when no net change occurs in the amount of liquid or vapor because the two opposite processes exactly balance each other. Copyright Cengage Learning. All rights reserved 31

Section 14.4 Evaporation and Vapor Pressure Concept Check Which of the following would be expected to have the highest vapor pressure at room temperature? a) CH 3 CH 2 CH 2 OH b) CH 3 CH 2 CH 2 NH 2 c) CH 3 CH 2 CH 2 CH 3 d) CH 3 CH 2 CH 3 Copyright Cengage Learning. All rights reserved 34

Section 14.5 The Solid State: Types of Solids Types of Crystalline Solids Ionic Solids ions at the points of the lattice that describes the structure of the solid. Molecular Solids discrete covalently bonded molecules at each of its lattice points. Atomic Solids atoms at the lattice points that describe the structure of the solid. Copyright Cengage Learning. All rights reserved 37

Section 14.6 Bonding in Solids Molecular Solids Fundamental particle is a molecule. Melt at relatively low temperatures. Held together by weak intermolecular forces. Copyright Cengage Learning. All rights reserved 41

Section 14.6 Bonding in Solids Atomic Solids Fundamental particle is the atom. Properties vary greatly. Group 8 low melting points Diamond very high melting point Copyright Cengage Learning. All rights reserved 42

Section 14.6 Bonding in Solids Bonding in Metals Metals are held together by strong, but nondirectional covalent bonds (called the electron sea model) among the closely packed atoms. Copyright Cengage Learning. All rights reserved 43

Section 14.6 Bonding in Solids Bonding in Metals Metals form alloys of two types. Substitutional different atoms are substituted for the host metal atoms. Copyright Cengage Learning. All rights reserved 44

Section 14.6 Bonding in Solids Bonding in Metals Metals form alloys of two types. Interstitial small atoms are introduced into the holes in the metallic structure. Copyright Cengage Learning. All rights reserved 45