# the properties of gases

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The Properties of Gases. 박영동 교수 자연과학대학 화학과. 기체는 왜 다루는가 ?. 역사적인 배경과 의미 Boyle’s Law – First Scientific Experiment, 1661 Charles’s Law – Definition of Temperature, 1780s Avogadro’s Hypothesis – - PowerPoint PPT Presentation

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The Properties of Gases

The Properties of Gases ? Boyles Law First Scientific Experiment, 1661Charless Law Definition of Temperature, 1780sAvogadros Hypothesis Combined Ideal Gas Law and Kinetic Theories First Successful Scientific Law derived from purely mathematical approach. , 1, 2 , - The perfect gas equation of state

Isotherms of an ideal gas and a real gas.

Boyles law in 1660.

an ideal gas and a real gas

pressure is the force F acting on an area AN/m2 = Pa(pascal)1 atm = 1.013105 Pa = 760 torr1 bar = 1105 PaThe perfect gas equation of state

Charless law in 1780s.

Charless law and a perfect gasAvogadros principle in 1811.The molar volume of various gases at SATP(RT, 1bar), dm3 mol-1 Perfect gas24.7896He24.8Ar24.4H224.8N224.6O224.8NH324.8The gas constant, R8.31447JK-1mol-18.2057410-2LatmK-1mol-11.98721calK-1mol-1Pressure and partial pressure

Partial pressure of idea gases

Daltons concept of partial pressure in 1801.Kinetic model of an ideal gasMaxwell distribution of speeds

an ideal gas in a container of side lBasic assumptions:

very small particles, all with non-zero mass. in constant, random motion.perfectly elastic collisions with the walls.negligible interactions among molecules except collisions.The total volume of the gas molecules is negligible.The molecules are perfectly spherical in shape, and elastic.no relativistic effects. no quantum-mechanical effects. instant collision with the wall.The equations of motion of the molecules are time-reversible.

Kinetic model of an ideal gas for basicsClick here to see KineticTheory_of_Gas.pdf Maxwell distribution of speeds

Maxwell distribution of speeds

c(mp)422 c476 c(rms)517 Diffusion, Effusion

(a) Diffusion, (b) EffusionEffusion when diameter is smaller than the mean free path .Effusion rate is proportional to speed of molecules, and area of a small hole.Effusion rate c (T/M)1/2 Molecular Collisions

cross sectional area = d2

sweep volume= c ccollision rate z =c number density of molecule = 21/2NAcp/RTmean free path = RT/(21/2NAp)number density of molecules = N/V = nNA/V = pNA/RT collision cross-section/nm2Ar0.36C2H40.64C6H60.88CH40.46Cl20.93CO20.52H20.27He0.21N20.43Ne0.24O20.40SO20.58Real Gases

potential energy variationInteraction between moleculesInteractionsphase transitionfinite sizes of molecules

Isotherms of CO2Phase transition and the critical temperatureCritical TemperatureCO2 at the pressure of 75 atm31 http://www.youtube.com/watch?v=8ZbZVikZP9w&feature=related

Compression Factor, Z

Compression factor at 0

The van der Waals equation of state

volume effectsize effectaccessible volume is smaller than the physical volume due to the molecular volume.

interaction effectpressure measured is smaller than the ideal pressure due to the attractions between molecules.

van der Waals correction to

The van der Waals equation

van der Waals isotherms

interpretation of the van der Waals equation

at critical point,

van der Waals coefficientsa/(atm dm6 mol- 2)b/(10-2 dm3 mol-1)Ar1.3373.20CO23.6104.29He0.03412.38Xe4.1375.16The liquefaction of gases

The principle of the Linde refrigerator.The van der Waals gas and Boyle TemperatureZ=0 at Boyle temperature TB,B = b - a/RT = 0

van der Waals coefficientsTB (K)a/(atm dm6 mol- 2)b/(10-2 dm3 mol-1)vdW(a/bR)expAr1.3373.20509411.5CO23.6104.291025714.8He0.03412.3817.522.64Xe4.1375.16977405.9

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