Graham's Law of Diffusion of Gases
Statement
The rate of diffusion or effusion of a gas is inversely proportional to the square root of its density at constant temperature and pressure.
Mathematical Form
Let us have two gases 1 and 2, having rates of diffusion as r₁ and r₂ and densities as d₁ and d₂ respectively.
According to Graham's law,
Demonstration of Graham's Law
This law can be verified in laboratory by noting the rates of diffusion of two gases in a glass tube, when they are allowed to move from opposite ends.
Two cotton plugs soaked in HCl and NH3 solutions are introduced in the open ends of 100 cm long tube simultaneously. HCl molecules travel a distance of 40.5 cm and NH3 molecules cover 59.5 cm. They produce dense white fumes of NH4Cl at point of junction. So,
1.46 = 1.46
Hence, the law is verified.
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