Lec-24-11-1P - Chapter 11 Liquids Solids and Materials...

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1 1 Chapter 11: Liquids, Solids and Materials 2 How is this class going? A: insultingly easy B: its ok C: struggling but I’ll make it D: I’m worried E: this is a class?
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2 3 The Liquid State A liquid forms when a gas condenses. •This occurs at low T (and/or high P ). Average intermolecular attraction > avg E k . Molecules are close together and in constant motion They have a distribution of speeds (and E k ) A few have enough E k to slide past each other. 5 The Liquid State Viscosity Viscosity = Resistance to flow. High viscosity = slow flow. low viscosity: water, ethanol, gasoline… high viscosity: honey, corn syrup …
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3 6 High viscosity is caused by: Large intermolecular attractions. Large entanglement of molecules. Higher T = lower viscosity E k > E barrier required to move past another molecule. • Increase T = increase average E k . More molecules have E k > E barrier The Liquid State 7 Liquid molecules attract each other. Surface molecules experience unbalanced forces . They are not as well stabilized. Smaller surface area higher stability. The Liquid State: surface properties
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4 8 Raindrops are spherical ( surface/ V ratio minimized ). Surface tension Surface tension = E required to form a flat surface. Substance Formula Surface Tension J/m 2 at 20°C Octane C 8 H 18 2.16 x 10 -2 Ethanol C 2 H 5 OH 2.23 x 10 -2 Chloroform CHC l 3 2.68 x 10 -2 Benzene C 6 H 6 2.85 x 10 -2 Water H 2 O 7.29 x 10 -2 Mercury Hg 46. x 10 -2 The Liquid State 9
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5 10 The Liquid State Surface tension Surface tension = E required to form a flat surface. “Cloud Gate”, Chicago Hg 11
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6 12 The “winner” depends on the amount of liquid and any surface/liquid attractions . A drop of water: puddles on a dirty surface “beads” on a waxy surface Why don’t all liquids form spheres in all cases? It’s a balancing act … Gravity pulls down (giving a puddle). Surface tension contracts (into a sphere).
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