The Properties of Gases

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# The Properties of Gases - PowerPoint PPT Presentation

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 –

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### The Properties of Gases

박영동교수

자연과학대학 화학과

기체는 왜 다루는가?

역사적인 배경과 의미

Boyle’s Law – First Scientific Experiment, 1661

Charles’s Law – Definition of Temperature, 1780s

Combined Ideal Gas Law and Kinetic Theories– First Successful Scientific Law derived from purely mathematical approach.

실용적인 배경과 의미

기체는 열역학의 기초, 열역학 제1, 2 법칙을 설명

화학 평형, 화학적 퍼텐셜의 기초

화학반응의 근본적 이해를 도움- 반응동력학

기체를 다루는 공정 이해에 중요한 기초를 줌

The perfect gas equation of state

pressure is the force F acting on an area A

N/m2 = Pa(pascal)

1 atm = 1.013×105 Pa = 760 torr

1 bar = 1×105 Pa

Boyle’s law in 1660.

Isotherms of an ideal gas and a real gas.

an ideal gas and a real gas

The perfect gas equation of state

Charles’s law in 1780s.

Charles’s law and a perfect gas

Pressure and partial pressure

Dalton’s concept of partial pressure in 1801.

Partial pressure of idea gases

Kinetic model of an ideal gasMaxwell distribution of speeds

Basic 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.

an ideal gas in a container of side l

Kinetic model of an ideal gas for basics

Diffusion, Effusion
• Effusion when diameter is smaller than the mean free path λ.
• Effusion rate is proportional to speed of molecules, and area of a small hole.

Effusion rate ∝c∝(T/M)1/2

(a) Diffusion, (b) Effusion

Molecular Collisions

number density of molecules = N/V = nNA/V = pNA/RT

‘c’

sweep volume= ‘c’ σ

collision rate z =‘c’ σ × number density of molecule

=21/2NAσcp/RT

mean free path λ= RT/(21/2NAσp)

cross sectional area σ= πd2

Real Gases

Interactions

phase transition

finite sizes of molecules

Phase transition and the critical temperature

Interaction between molecules

potential energy variation

Isotherms of CO2

Critical Temperature

31 ℃

CO2 at the pressure of 75 atm

Compression Factor, Z

Compression factor at 0 ℃

The van der Waals equation of state
• van der Waals correction to

size effect

accessible volume is smaller than the physical volume due to the molecular volume.

interaction effect

pressure measured is smaller than the ‘ideal’ pressure due to the attractions between molecules.

volume effect

The van der Waals equation
• at critical point,

van der Waals isotherms

interpretation of the van der Waals equation

The liquefaction of gases

The principle of the Linde refrigerator.

The van der Waals gas and Boyle Temperature
• Z=0 at Boyletemperature TB,
• B = b - a/RT = 0