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Understanding Viscosity and Surface Tension in Liquids

Viscosity refers to a liquid's resistance to flow, with high viscosity indicating significant resistance. It is influenced by intermolecular forces (IMFs) and decreases with rising temperature. Surface tension, the energy needed to increase a liquid’s surface area, reflects the "tightness" of the surface. Water exhibits high surface tension due to hydrogen bonding. Concepts such as cohesive and adhesive forces play crucial roles in phenomena like meniscus formation and capillary action, essential for water movement in plants through xylem.

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Understanding Viscosity and Surface Tension in Liquids

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  1. Some Properties of Liquids viscosity: a liquid’s resistance to flow -- high viscosity = high resistance to flow -- depends on IMFs -- as temp. increases, viscosity decreases

  2. Molecules on a liquid’s surface experience a net inward force -- this reduces surface area and “packs together” m’cules on surface surface tension: the energy required to increase a liquid’s surface area by 1 m2 -- a measure of the “tightness” of a surface’s “skin” -- water has a high surface tension due to HBFs

  3. meniscus: H2O meniscus: Hg cohesive forces: IMFs that bind... similar m’cules to each other a substance to a surface adhesive forces: IMFs that bind... -- their relative magnitude determines the shape of a meniscus adhesion cohesion > adhesion cohesion <

  4. In green plants, capillary action draws water through narrow tubes, collectively called xylem. capillary action: the rise of liquids up narrow tubes “stretches” -- adhesion _________ the liquid, while cohesion… keeps it together

  5. Why does liquid go up narrow tubes farther than up thick tubes? adhesion force 2pr gravity pr2 = gravity If tube diameter increases by a factor of 10: adhesion increases 10X; liquid’s weight increases 100X. Liquid stops rising under this condition.

  6. Will a “plug” of liquid continue inching its way up a tube? Assume there is a plug that wants to break free… Adhesion forces pull it up. As soon as plug breaks free from rest of liquid, “down” adhesion forces appear, which equal “up” adhesion forces. But there’s also gravity, so “down” wins. Plug drops until “up” adhesion equals gravity. “No creeping plugs.”

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