Question

Difficulty: EasyGraham's Law of Diffusion and Effusion

Given that the molar mass of methane (CH4CH_4) is 16 g/mol16\text{ g/mol} and that of sulfur(IV) oxide (SO2SO_2) is 64 g/mol64\text{ g/mol}, what is the ratio of the rate of diffusion of methane to that of sulfur(IV) oxide under identical conditions of temperature and pressure?

  1. 2:12 : 1Answer
  2. B
    4:14 : 1
  3. C
    1:21 : 2
  4. D
    1:41 : 4

Answer

2:12 : 1
According to Graham's Law of Diffusion, the rate of diffusion of a gas is inversely proportional to the square root of its molar mass (r1Mr \propto \frac{1}{\sqrt{M}}). Comparing methane (CH4CH_4, M=16 g/molM = 16\text{ g/mol}) to sulfur(IV) oxide (SO2SO_2, M=64 g/molM = 64\text{ g/mol}), the ratio of their rates is 6416=4=2\sqrt{\frac{64}{16}} = \sqrt{4} = 2. Therefore, methane diffuses twice as fast as sulfur(IV) oxide, yielding a ratio of 2:12 : 1.

Step-by-Step Solution

1
State Graham's Law of Diffusion formula
r1r2=M2M1\frac{r_1}{r_2} = \sqrt{\frac{M_2}{M_1}}
The rate of diffusion of a gas is inversely proportional to the square root of its molar mass.
2
Substitute the given molar masses into the formula
rCH4rSO2=6416\frac{r_{CH_4}}{r_{SO_2}} = \sqrt{\frac{64}{16}}
Molar mass of SO2=64 g/molSO_2 = 64\text{ g/mol} and molar mass of CH4=16 g/molCH_4 = 16\text{ g/mol}.
3
Simplify the ratio
rCH4rSO2=4=2\frac{r_{CH_4}}{r_{SO_2}} = \sqrt{4} = 2
Taking the square root of 4 gives 2, which corresponds to a ratio of 2:12 : 1.

Key Concept

Graham's Law of Diffusion
Estimated Time:45s
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