Question:1. Write down the comparisons of diffusion and effusion:

Ans.: Similarity:

1. Both the processes are spontaneous transfer gas and liquid molecules.

2. Transfer of molecules takes place from an area of high pressure or high densi concentration to lower ones in both of the processes.

3. In both of processes the final pressure or concentration or density of matter becom.


Question:2. State Graham’s diffusion law with mathematical explanation.

              Or, From this (law) how will you determine molecular weight of an unknown gas?

Ans.: Thomas Graham in 1829 performed a good deal of experiment and discovered a law. which, after his name, is called Graham’s law of diffusion.

Graham’s law of diffusion: According to Thomas Graham,” At constant temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its density.” Mathematical explanation: If ‘r’ is the rate of diffusion and ‘d’ is the density of a gas, then,

If we consider r1 & r2 be the rate of diffusion of two gases having density d1 & d2 respectively, then we get-

to the square roots of its density or molecular mass. Equation (iii) and (iv).

Determining molecular mass of an unknown gas from Graham’s law: If the rates of diffusion of two gases are rı & r2 and the molecular mass of the known gas is M1 and unknown gas is M2 then, we can calculate the molecular mass of the unknown gas from the equation – (iv).

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