Presentation on theme: "Chpt 5 - Gases Gas Law Development Dalton’s Partial pressure law"— Presentation transcript:
1 Chpt 5 - Gases Gas Law Development Dalton’s Partial pressure law Graham’s effusionKinetic TheoryRoot-mean-square velocityvan der Waals equation of stateHW: Chpt 5 - pg , #s 5, 22, 23, 25, 31, 32, 35, 39, 41, 46, 55, 64, 66, 71, 75, 77, 81, 91, 95, 97, 101, Due Mon 10/4
2 Torricelli barometer Pressure is? Units? The height in mm of mercury above the surface of the resevoirof mercury determines the pressure.The units are mmHg.mmHg is also the same unit asTorr. i.e. standard pressure is 760 mmHg and 760 Torr
3 Simple Manometer Similar to the barometer, the height difference of the Hg relates the pressure difference in the unknown gas bulb side to the current atmospheric pressure.The higher Hg side has the _____ pressure.(higher/lower)
4 Boyle’s LawConstant temperature experiments demonstrated the PV=constant graphing this yields an inverse relationshipThus if the pressure of volume changes at a constant temperatureP1V1 = P2V2
5 Plot of PV vs. P for Several Gases This graph shows Boyles linear relationship for the PxV. The constant depends on the gas
6 Charles’s LawConstant pressure experiments demonstrated that Volume is directly proportional to Temperature (Kelvin)V1 = V2T T2Several gases were used & all extrapolate to zero volume and the same temperature at negative 273oC
7 Plots of V vs. T(ºC) Charles’s Law Experiment results Demonstrates a unique absolute zero at oC
8 Combined Gas Law P1V1 = P2V2 T1 T2 Avogadro’s Law - equal volumes of gas contain equal particles of gasV = k nAt constant temperature and pressure the volume is directly proportional to the number of moles of gas.
9 Ideal Gas LawPutting it all together, we can calculate that constant now. The universal gas constant R.PV=R or PV=nRTnT R = l *atm/mol*K= l *kpa/mol*K
10 Density / Molar Mass with Ideal gas law Molar mass, MM = ? What are the units?So, moles = ?Density, d = ? Use L for density since gasSo, mass = ?Combine and get expression for moles n=N= PV = dV Thus MM = dRT volume will be in LitersRT MM P
11 Dalton’s Law of Partial Pressures The gases in a mixture act independently and thus the forces (and pressures) are additive.Ptotal = P1 + P2 + P3 + …
12 Kinetic Molecular Theory Ideal Gas BehaviorParticles assumed to have zero volumeParticles in constant motionParticles exert no forces on each otherKEave is directly proportional to T (K)Check out Appendix 2 to see derivation of ideal gas law PV=nRT
13 Kinetic Theory also KEave = 3/2 RT Root square mean velocity urms = sqrt(3RT/M)Where M is mass of a mole in kgSo now we can calculate ave velocities of gases
14 Effusion of Gas into Evacuated Chamber If more than one type of gas or more than one isotope, which gas effuses faster?Lighter gas movesFaster!!KE = 1/2 mv2
15 Relative Molecular Speed Distribution of H2 and UF6
16 Diffusion Rates of NH3 and HCl Molecules Through Air Relative diffusion/effusion rate pg. 213 textbookrate1 = Sqrt(M2)rate2 Sqrt(M1) lighter gas is faster
17 Ideal vs. Real GasesAll of the gases are real!!! They just behave “ideally” at certain temperatures and pressures.Think of the KMT assumptions, what conditions would gases “fail” to act ideally.Low temperatures (gases condense) & High pressures (force the gases together so they have to interact)
19 Plot of PV/nRT vs. P for N2 Gas This graph shows that at higher temperatures gases behave closer to ideal even at high pressures.Recall that gases behave “ideally” at low pressures and high temperatures.
20 van der Waals Equationvan der Waals equation is entire gas law relationship with corrections for real volume and molecular attractions. pg.216 textbook with Table 5.3 for some common gases(Pobs + correction) x ( V - nb) = nRTThis formula is also given on AP exam sheet.
21 Values of the van der Waals Constants for Common Gases a is a measure of intermolecular attractions (it is the correction to the pressure to account for attractions for each other)b is a measure of size of the molecule (it is the volume correction)