6.2 Chapter 12 Liquids and Solids (6 per page)

6.2 Chapter 12 Liquids and Solids (6 per page) - 15/02/2011...

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15/02/2011 1 Chapter 12: Liquids, Solids and Intermolecular Forces Objectives Understand how intermolecular forces give rise to liquid properties: surface tension, wetting, capillary rise, viscosity Examine phase transitions enthalpy changes, vapor pressure, boiling, melting, sublimation. Interpretation of Phase Diagrams 12-1 Intermolecular Forces Br 2 What is different about the Br 2 molecules in the liquid phase and the gas phase? Molecules in the gas phase are essentially 12-1 Intermolecular Forces Br 2 independent. Very few interactions with each other. 12-1 Intermolecular Forces Molecules in liquid phase governed by attractive interactions between each other and with container and with container. Br 2 12-1 Intermolecular Forces Cohesive: like molecules. Adhesive: unlike molecules. Cohesive Adhesive Br 2
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15/02/2011 2 12-1 Intermolecular Forces 12-2 Some Properties of Liquids Cohesive interactions hold drops of liquid together. Cause them to be spherical. 12-2 Surface Tension Molecules in the interior can form a maximum number of favourable interactions surface interior interactions (cohesive). Molecules at the interface with a gas (like air) can form fewer interactions. 12-2 Surface Tension Much more empty space in surface interior the gas, less opportunity to interact. 12-2 Surface Tension Molecules would prefer to be in the interior than at the surface. Liquid will adopt th h ith surface interior the shape with the smallest possible surface area. The sphere has the lowest surface area to volume ratio of any shape. 12-2 Surface Tension It takes energy to increase the surface area of a liquid. Surface Tension: energy area 2 2 O H 10 28 . 7 2 m J (20 C, decreases with temperature)
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15/02/2011 3 12-2 Surface Tension It takes energy to increase the surface area of a balloon. The surface of the balloon is stretched i.e. under tension. Surfaces of liquids are similar. 12-2 Wetting Liquid at the solid interface interacts with the solid. Strength depends on which liquid and solid are involved. Adhesive interactions. Adhesive 12-2 Wetting Greased glass plate. Few favourable interactions between water and grease. Interface with solid is similar to interface with air. 12-2 Wetting Cohesive interactions > Adhesive interactions Drops of liquid are close to spherical. Water does not wet a greased surface. 12-2 Wetting Clean glass plate. Favourable interactions between water and glass. Cohesive Adhesive interactions 12-2 Wetting Water spreads out to increase the interface with the glass. Water wets a clean glass surface.
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15/02/2011 4 12-2 Meniscus Concave meniscus. Favourable interactions meniscus between water and glass.
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This note was uploaded on 04/04/2011 for the course SCIENCE CHEM 120 taught by Professor Fenster during the Winter '11 term at McGill.

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6.2 Chapter 12 Liquids and Solids (6 per page) - 15/02/2011...

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