Question

Rank the following gases in order of decreasing rate of effusion. Rank from the highest to lowest effusion rate. To rank items as equivalent, overlap them.
F2 He C5H10 H2 PH3

Answer 1

Answer:

H2, He, PH3, F2, C5H10

Explanation:

From Graham's law, we understood that lighter gas will diffuse faster than heavier gas under same condition. Graham's law of diffusion states as follow:

The rate (R) of diffusion of a gas is inversely proportional to the square root of its density (D) provided temperature and pressure remains constant. Mathematically, it is represented as:

R & 1/√D

Recall:

Molar Mass (M) = 2 x vapour density (D)

M = 2D

R & 1/√M

From the above, we can see that the rate is inversely proportional to the square root of the molar mass of substance. This implies that lighter gas will diffuse faster.

Now, to rank the above from the highest to rate rate of effusion, let us determine the molecular weight of each substance. This is illustrated below:

Molar Mass of F2 = 19 x 2 = 38g/mol

Molar Mass of He = 4g/mol

Molar Mass of C5H10 = (12X5) + (10X1) = 70g/mol

Molar Mass of H2 = 2x1 = 2g/mol

Molar Mass of PH3 = 31 + (3x1) = 34g/mol

Now, we can rank the substance beginning from the highest to the lowest rate of effusion as follow:

Substance >> Molar Mass >> Rank

H2 >>>>>>>>> 2g/mol >>>>>> 1

He >>>>>>>>> 4g/mol >>>>>> 2

PH3 >>>>>>>> 34g/mol >>>>> 3

F2 >>>>>>>>>> 38g/mol >>>> 4

C5H10 >>>>>> 70g/mol >>>> 5