Gases and Kinetic-Molecular heory: Chapter Chapter Outline Comparison of Solids, Liquids, and Gases Composition of the Atmosphere and Some Common Properties of Gases Pressure Boyle s Law: he Volume-Pressure Relationship Charles Law: he Volume-emperature Relationship; he Absolute emperature Scale Standard emperature and Pressure he Combined Gas Law Equation Chapter Outline Avogadro s Law and the Standard Molar Volume Summary of Gas Laws: he Ideal Gas Equation Determination of Molecular Weights and Molecular Formulas of Gaseous Substances Dalton s Law of Partial Pressures Mass-Volume Relationships in Reactions Involving Gases he Kinetic-Molecular heory Diffusion and Effusion of Gases Real Gases: Deviations from Ideality
Comparison of Solids,Liquids, and Gases he density of gases is much less than that of solids or liquids. Densities (g/ml) H O Solid 0.97 Liquid 0.998 Gas 0.000588 CCl 4.70.59 0.00503 Composition of the Atmosphere and Some Common Properties of Gases Composition of Dry Air 78.09 0.93 0.00 Gas % by Volume N O 0.94 Ar CO 0.03 He, Ne, Kr, Xe CH 4 0.0005 H 0.00005 Properties of Gases All gases have several properties in common Relatively low density Easily compressed Expand without limits to fill the volume of any container Described by temperature,volume, and the moles present
Ideal Gases An ideal gas is defined as one for which both the volume of the molecules and the forces between the molecules are so small that they have no effect on the behavior of the gas. Ideal Gases Huge number of molecules Point masses, no volume No forces between molecules Constant, chaotic/random motion Elastic collisions ( billiard balls ) Pressure Dimensions of force/area SI unit is N/m, or Pascals Other more common units: atmospheres: atm = 0,35 Pa torr (mm Hg): 760 torr = atm lbs/in : 4.7 psi = atm 3
Pressure Force (gas collisions with surface) P = F A Pressure Area (over which force acts) ABC s of the Gas Law ABC Avogadro s Law Charles Law Boyle s Law Gas Laws Boyle s Law (~660) P V = Constant or P V = PV (at constant n and ) 4
emperature We find that as 0, then V 0 MUS use absolute temperature (Kelvin, NO C) 0 C = 73.5 K K = C + 73.5 Gas Laws Charles Law (~787) V = Constant or V V = (at constant n and P) Standard emperature and Pressure Standard temperature and pressure is given the symbol SP. It is a reference point for some gas calculations. Standard P.00000 atm or 0.3 kpa Standard 73.5 K or 0.00 o C 5
Gas Laws Avogadro s Law states that at the same temperature and pressure, equal volumes of two gases contain the same number of molecules (or moles) of gas. If we set the temperature and pressure for any gas to be SP, then one mole of that gas has a volume called the standard molar volume. he standard molar volume is.4 L at SP. his is another way to measure moles. For gases, the volume is proportional to the number of moles. Gas Law Avogadro V = Constant n or N V N = V (at constant P and ) Combined Gas Law he Ideal Gas Law P V = Constant n or PV = nr 6
Combined Gas Law Universal Gas Constant SI units: R = 8.34 J mol K Alternative units: R= 0.0806 L atm mol K = 6.36 L torr mol K Ideal Gas Law Any gas will behave ideally in the limits of Low Pressure High emperature Explain these limits in terms of previous definition and properties? he Ideal Gas Law Ideal gas law OK for most gases at ordinary, P MUS fail at some point, since solids and liquids exist. Deviations at high P, low. meaning of high and low here depends on the identity of the gas 7
he Ideal Gas Law How much volume for one mole of an ideal gas at 0 C and atm (SP)? = (73 K/ atm) x (0.08 L atm mol - K - ) x ( mol) =.4 L/mol (Note: this result doesn t depend on the gas involved. At the same temperature and pressure, equal numbers of molecules of all ideal gases occupy the same volume.) Using the Ideal Gas Law PV PV = nr or = nr P V PV = Constant (for same number of moles present) Using the Ideal Gas Law A sample of Neon has a volume of 00 L at 5 o C and a pressure of 985 torr. What volume would the gas occupy at 0 o C and 760 torr? V =00 L, P =985 torr, =98 K V =?, P =760 torr, =73 K 8
Using the Ideal Gas Law A sample of Neon has a volume of 00 L at 5 o C and a pressure of 985 torr. What volume would the gas occupy at 0 o C and 760 torr? P V PV = or PV V = P Using the Ideal Gas Law Which bulb contains the largest number of atoms? Which bulb contains the greatest mass of atoms? He.0 L 0.50 atm 300 K Ne.0 L 0.40 atm 300 K Ar.0 L 0.0 atm 300 K Using the Ideal Gas Law A Helium filled weather balloon with a diameter of 4 ft has a volume of 740 ft 3. How many grams of Helium are required to fill the balloon to 745 torr at o C? ( ft 3 = 8.3 L) 9
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