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6.2 Chapter 12 Liquids and Solids (6 per page)

6.2 Chapter 12 Liquids and Solids (6 per page) - Objectives...

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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 E i h t iti 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 t th 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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