ch. 12 notes

ch. 12 notes - 1. Compar ison of solids, liquids, and...

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Unformatted text preview: 1. Compar ison of solids, liquids, and gasses Fluids f low freely Condensed states have higher density than gas Vapor refers to a gas that is formed by evaporation of a liquid or sublimation of a solid Volatile liquids are easily converted to gas at room temperature. All gasses are miscible-- they do not mix completely with one another, unless they react with each other 2. Composition of the Atmosphere and some common properties of gasses Gasses can be compressed into smaller volumes o Their densities can be increased by applying increased pressure Gasses exert pressure on their surroundings o Pressure must be exerted to the confined gas Gasses expand without limit o Therefore they occupy the volume of any container Gasses diffuse into one another o So they mix complete in containers o They do not separate on standing The amounts and properties of gasses are described in terms of temperature, pressure, volume occupied, and number of molecules present 3. P ressure Pressure is force per unit area Barometer is used to measure atmospheric pressures Manometer is a glass U-tube partially filled with mercury Atmospheric pressure varies with atmospheric conditions and distance above sea level The average sea-level atmospheric pressure is called standard pressure = 760 mm Hg Other definitions of standard pressure: o 76 cm Hg o 760 mm Hg o 760 torr o 1 atmosphere o 101.3 kPa 4. Boyle's Law: The Volume-P ressure Relationship PV=k (constant n, T) The volume of a fixed quantity of gas (at constant temperature) is inversely proportional to the pressure At normal temperatures and pressures, most gasses obey Boyle's Law--this is called ideal behavior P1V 1=P2V 2 (for a given amount of a gas at a constant temperature) 5. Charles's Law: The Volume-Temperatu re Relationship; The Absolute Temperatu re Scale At constant pressure, the volume occupied by a definite mass of a gas is directly proportional to its absolute temperature V= kT V 1/T1=V 2/T2 (for a definite mass of gas at constant pressure) 6. Standard Temperatu re and P ressure Exactly 0 degrees Celsius and one atmosphere of pressure P1V 1/T1 = P2V 2/T2 (constant amount of gas) 7. The Combined Gas Law Equation 8. Avogadro's Law and Standard Molar Volume At the same temperature and pressure, equal volumes of all gasses contain the same number of molecules Avogadro's Law: At constant temperature and pressure, the volume, V, occupied by a gas sample is directly proportional to the number of moles, n of gas. o V=kn V 1/n1 = V 2/n 2 (constant T, P) STP = 22.414 li ters per mol 9. Summa ry Ideal gas is one that exactly obeys these gas laws PV=nRT o R=.08206 Latm/molK o R = 8.314 J/molK o R = 8.314 kgm 2/s2Kmol Determination of Molecular Weights and Molecular Formulas of Dalton's Law of Pa rt ial P ressures 10. 11. Gaseous Substances The total pressure exerted by a mixture of ideal gases is the sum of the partial pressures of those gases. o Ptotal = PA + PB + PC + ..... Mole fraction: o X A = part/whole o PA = X A Ptotal 12. M ass-Volume Relationships in Reactions I nvolving Gases At constant pressure and temperature, the volumes of reacting gasses can be expressed as a ratio of simple whole numbers Mole coefficients serve as volume amounts The Kinetic-Molecular Theory 13. Gasses consist of discrete molecules o Individual molecules are small and far apart The gas molecules are in continuous, random, straight-line motion with varying velocities Collision between gas molecules and the wall are elastic o Total energy is energy gained/lost Molecules exert no attractive or repulsive forces on one another between collisions o Each molecules t ravels in a straight-line with constant velocity Average kinetic energy of gas molecules is directly proportional to the absolute temperature of the sample Average molecular speed = average velocity times square root of T/molecular weight (GO BACK AND REVIEW P. 440-443) 14. Diffusion and Effusion of Gasses Effusion is the escape of a gas through a tiny hole Diffusion is the movement of a substance into a space or the mixing of one substance with another 15. Deviations from I deal Gas Behavior PV/nRT should equal 1.0 for an ideal gas Non ideal gas behavior is most significant at high pressures and/or low temperatures...close to conditions that liquefy gases van der Waals equation: (P + ((n^2)a)/V^2)(V-nb)=nRT Dispersion forces result from short-lived electrical dipoles produced by the attraction of one atom's nucleus for an adjacent atom's electrons. ...
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This note was uploaded on 04/28/2008 for the course CHEM 1212 taught by Professor Suggs during the Spring '08 term at UGA.

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