20-Liquids, Solutions, and Solids

20-Liquids, Solutions, and Solids - Liquids, Solutions, and...

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Liquids, Solutions, and Solids B. A. Rowland 53750/53760 Comparing the States of Matter Let us take a molecular-level view of the three phases of matter (you can see this diagram on slide 3 of this lecture). Gas : Lots of space between gas particles and low IMFs (due to those large distances). Particles are in random motion. Most disordered phase of matter. Liquid : No space between liquid particles (a condensed phase of matter—liquids are in general incompressible) and high IMFs (due to small distances). Particles are in random motion. Liquids are intermediately ordered phase of matter (characteristics of both gases and solids). Solid : No space between solid particles (a condensed phase of matter—solids are in general incompressible) and high IMFs (due to small distances). Particles vibrate around a fixed point in space (in effect, they are nearly motionless). The most ordered phase of matter. An example of the volume difference between phases: 1 mole of water vapor at 298 K and 1 atm would occupy a volume of 24.5 L (that’s over 12 2-L soda bottles). One mole of liquid or solid water at these conditions would fit in your mouth! Phase Transitions You should know the names of the six phase transitions and how to change between phases with pressure and temperature. Solid Liquid: Melting Liquid Solid: Freezing Solid Gas: Sublimation Gas Solid: Deposition Liquid Gas: Vaporization Gas Liquid: Condensation When you increase temperature OR decrease pressure you move solid liquid gas. When you decrease temperature OR increase pressure you move gas liquid solid. Liquids There are many examples of liquids each exhibiting some neat property (capillary action, viscosity, etc). The great variety of liquids and their ensuing behaviors are due to the IMFs acting between the molecules in the sample! Some key facts to remember about
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liquids is that they: i) are more disordered than solids but less so than gases; and ii) have temperature-dependent vapor pressures. Writing an equation of state for a liquid is not a simple task (as it is for an ideal gas), as the close proximity of liquid molecules causes high IMFs on the liquid molecules. They are also in random motion, so you have to account for both complex paths AND IMFs in a liquid; this make the problem very difficult mathematically (however, there are models—they are just beyond the scope of what we are learning now)! IMFs in Liquids Review lecture on Intermolecular Forces for more information. Properties of Liquids Here are definitions of the properties of liquids we are interested in: Capillary Action (CA): The spontaneous rising of a liquid through a narrow tube. Viscosity (Vis): The resistance of a liquid to flow. Surface Tension (ST):
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20-Liquids, Solutions, and Solids - Liquids, Solutions, and...

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