Physical Principles — Gas Laws

Historical · V4 (2023) → W.i 1 exam appearance

2013B Q12

Exam question

Explain the following laws:
a. Dalton’s
b. Boyle’s
c. Henry’s
d. Graham’s
e. Fick’s Law of Diffusion

CICMWrecks answer

Master answer

Dalton’s Law (of partial pressures)

P_{total}\;=\;P_{1}\;+\;P_{2}\;+\;P_{3}\;+\;.\;.\;.\;+P_{n}\;\equiv\;\sum_{i=1}^{n}\;P_{i}

The total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases.

Boyle’s Law

P\;\propto\;{1\over V}

The pressure exerted by a gas is inversly proportional to the volume it occupies, assuming the amount of gas and the temperature is constant

Henry’s Law

p\;=\;k_{H}\;c

where c=solubility of a gas at a fixed temp, k=Henry’s Law (equilibrium) constant p = partial pressure of the gas

Given a constant temperature, the amount of gas dissolved in a liquid, is proportional to the partial pressure of that gas

Graham’s Law

Diffusion\;\propto\;{1 \over \sqrt{MW}}

The rate of diffusion of a molecule is inversely proportional to the square root of its molecular weight

Fick’s Law of Diffusion

Diffusion \propto \;Diffusion\;Coefficient\;\:{(Concentration\;gradient\;×\;Surface\;area) \over Thickness}

Diffusive flux goes from a high-concentration area to a low-concentration area proportional to both the concentration gradient and surface area and is inversely proportional to the thickness of the membrane.

JC / Sakurai 2016

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Formulae used in this answer

Boyle’s Law

CWF-0001

P\;\propto\;{1\over V}

Dalton’s Law (of partial pressures)

CWF-0002

P_{total}\;=\;P_{1}\;+\;P_{2}\;+\;P_{3}\;+\;.\;.\;.\;+P_{n}\;\equiv\;\sum_{i=1}^{n}\;P_{i}

Fick’s Law of Diffusion

CWF-0003

Diffusion \propto \;Diffusion\;Coefficient\;\:{(Concentration\;gradient\;×\;Surface\;area) \over Thickness}

Graham’s Law

CWF-0004

Diffusion\;\propto\;{1 \over \sqrt{MW}}

Henry’s Law

CWF-0005

p\;=\;k_{H}\;c

Answer by JC, Sakurai

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Exam	Exact exam wording	Candidate success
2013B Q12	Explain the following laws: a. Dalton’s b. Boyle’s c. Henry’s d. Graham’s e. Fick’s Law of Diffusion	—