Chapter_11_Part_2 - Chapter 11: States of Matter: Liquids...

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Chapter 11 Part 2 1 of 7 Chapter 11: States of Matter: Liquids and Solids Part 2 Liquid State 1. Properties of Liquids: Surface Tension and Viscosity We have studied two properties of liquids thus far: vapor pressure and boiling point. Now we examine two additional properties. a. Surface Tension Surface tension is the energy required to increase the surface area of a liquid by a unit amount. Several phenomena are related to surface tension: i. the observation of what appears to be a film on the surface of a liquid a needle that is more dense than water can be suspended on the surface of the water the same needle would not float in the body of the water See figures to the right (top and side views) ii. capillary rise a liquid will rise in a very narrow diameter column the curve of the top of the liquid, the meniscus, depends on the attraction between the liquid and the column material o when the liquid is attracted to the column material the liquid curves down; you read the lower meniscus for the volume o when the liquid is not attracted to the column material, the liquid curves up; you read the upper meniscus for the volume o See figure below
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Chapter 11 Part 2 2 of 7 iii. formation of spherical drops a sphere gives the smallest possible surface area for a given volume) These three phenomena result from the unevenness of the forces within the liquid on molecules at the surface. A molecule within the body of the liquid experiences forces of attraction from other molecules that surround it. A molecule on the surface, however, has no molecules on top of it, so the net force on a surface molecule is toward the liquid. See the figure to the right. b. Viscosity Viscosity is the resistance to flow exhibited by liquids and gases. The figure to the right shows two different clear and colorless liquids. A steel ball was released into each at the same time. The graduated cylinder to the left contains a liquid with a higher viscosity (greater resistance) since that steel ball has traveled less distance. 2. Intermolecular Forces; Explaining Liquid Properties Intermolecular forces are forces between molecules. (The prefix inter– means between; the prefix intra– means within.) We will study three types of intermolecular forces. They are classified into two groups: van der Waals forces and hydrogen bonding. a. van der Waals Forces The term van der Waals refers to two types of intermolecular forces: 1. Dipole–Dipole Forces A dipole–dipole force is an attractive force that arises from the tendency of polar molecules to align with the partially positive end of one molecule near the partially negative end of another molecule. 2.
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This note was uploaded on 04/02/2008 for the course CHM 1220 taught by Professor Barber during the Fall '07 term at Wayne State University.

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Chapter_11_Part_2 - Chapter 11: States of Matter: Liquids...

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