chapter+12+Intermolecular+Forces

chapter+12+Intermolecular+Forces - Chapter 12...

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Chapter 12 Intermolecular Forces: solids, liquids and phase changes • 12.1-12.2 Phase changes and phase diagrams • 12.3 Types of intermolecular forces • 12.4-12.5 Properties of liquids – Uniqueness of water – Read at home The title slide for each chapter will tell you the sections you are responsible for! This means you will not be tested on 12.6 or 12.7 Back in chapter 1… • 3 physical states of matter • Kinetic vs. potential energy – Speed of particles vs Intermolecular attractions – Phase changes!!! microscopic Æ macroscopic • Gases chapter 4 – Huge distance between molecules • Solids/liquids here – Require knowledge of intermolecular forces
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Keeping track of molecular forces • Intramolecular forces: bonding forces within a molecule, influence chemical properties of a substance (reactivity) – Chemical properties of water same, no matter phase • Intermolecular forces: non-bonding forces between molecules, influence physical properties of a substance (mp, bp, phases ) – Physical properties of water differ greatly in different phases – Often weaker than covalent/ionic intramolecular forces, but are additive Types of Phase Changes • Phase changes are associated with intermolecular forces –g Æ l condensation l Æ g vaporization –l Æ s freezing s Æ l melting (fusion) – Sublimation : s Æ g, no liquid in between – Deposition : g Æ s, no liquid in between Fig 12.2 Enthalpy changes • For reactions at constant pressure, a thermodynamic variable is called enthalpy H= E+PV (see sec. 6.2) • The change in enthalpy ( Δ H): Δ H= Δ E+P Δ V Exothermic and endothermic processes: • An exothermic (“heat out”) process releases heat and results in a decrease in the enthalpy of the system • An endothermic (“heat in”) process absorbs heat and results in an increase in the enthalpy of the system accompany phase changes
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chapter+12+Intermolecular+Forces - Chapter 12...

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