Liquids and solids 2012

Liquids and solids 2012 - Properties of Liquids and Solids...

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Properties of Liquids and Solids David A. Katz Pima Community College Tucson, AZ
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Intermolecular Forces Affect Many Physical Properties The strength of the attractions between attractions between particles can greatly affect the properties affect the properties of a substance or solution.
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Viscosity ± Resistance of a liquid to flow is called to flow is called viscosity . ± It is related to the ease with which molecules can move past each other. ± Viscosity: ¾ Increases with stronger intermolecular forces ¾ Increases with the size of the molecules ¾ Decreases with Two methods of measuring viscosity: 1. Timing the flow of a liquid through an increasing temperature . opening. 2. A disk or drum type viscometer
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Viscosity Viscosity of hydrocarbons at 20°C Viscosity of hydrocarbons at 20 C
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Surface Tension Surface tension results from the net inward force experienced by the experienced by the molecules on the surface of a liquid.
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Surface Tension Drops of liquid on a coin How many drops of liquid can you put on a coin?
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Surface Tension Drops of liquid on a coin More on detergents and will be explained in the discussion of colloids
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Vapor Pressure Due to both temperature effects and energy transfers from collisions, molecules on the surface of a liquid are able to gain sufficient kinetic energy to escape into the atmosphere
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Vapor Pressure ±A t a n y t e m p e r a t u r e , s o m e m o l e c u l e s i n a l i q u i d h a v e enough energy to escape. ± As the temperature rises, the fraction of molecules that have enough energy to escape increases .
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Vapor Pressure If the container is open to the atmosphere, the molecules simply escape. This process is called This process is called evaporation . As molecules escape from the surface, they take energy with them resulting in a cooling effect on the liquid.
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Vapor Pressure A desert water bag (left) A desert canteen (center) An Army canteen (right)
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Vapor Pressure If the container is closed to the atmosphere, as more molecules escape the liquid, the pressure they exert increases.
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Vapor Pressure Eventually, the air space in the container becomes saturated with vapor molecules vapor molecules. The liquid and vapor reach a state of dynamic equilibrium : as liquid molecules evaporate, vapor molecules condense at the same rate . This is called the vapo pressure equilibrium This is called the vapor
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Which Will Evaporate First? What factors affect evaporation? Water methanol ethanol 2-propanol
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Which Will Evaporate First? What factors affect evaporation? Water methanol ethanol 2-propanol Effect of molecular weight Effect of molecular weight: H 2 O = 18 CH 3 OH = 32 C 2 H 5 OH = 46 C 3 H 8 OH = 60 Effect of polarity
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Vapor Pressure ±V a por pressure increases with temperature. ± When the vapor When the vapor pressure of a liquid equals the atmospheric pressure atmospheric pressure, the liquid boils.
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Liquids and solids 2012 - Properties of Liquids and Solids...

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