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Zorluk: KolayGraham's Law of Diffusion and Effusion

Under the same conditions of temperature and pressure, how many times faster will helium gas (He\text{He}) diffuse compared to methane gas (CH4\text{CH}_4)? [Relative atomic masses: H=1\text{H} = 1, C=12\text{C} = 12, He=4\text{He} = 4]

  1. 2 times fasterCevap
  2. B
    4 times faster
  3. C
    0.5 times as fast
  4. D
    8 times faster

Cevap

Helium gas diffuses 2 times faster than methane gas.
The rate of diffusion of a gas is inversely proportional to the square root of its molar mass (r1Mr \propto \frac{1}{\sqrt{M}}). Methane (CH4\text{CH}_4) has a molar mass of 16 g/mol16\text{ g/mol} and helium (He\text{He}) has a molar mass of 4 g/mol4\text{ g/mol}. Therefore, the ratio of the diffusion rate of helium to methane is 16/4=4=2\sqrt{16/4} = \sqrt{4} = 2.

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1
Calculate the molar masses of both gases.
Molar mass of He=4 g/mol\text{Molar mass of He} = 4\text{ g/mol}; Molar mass of CH4=12+(4×1)=16 g/mol\text{Molar mass of CH}_4 = 12 + (4 \times 1) = 16\text{ g/mol}.
Molar masses are required inputs for Graham's Law.
2
Apply Graham's Law formula: r1r2=M2M1\frac{r_1}{r_2} = \sqrt{\frac{M_2}{M_1}}.
rHerCH4=164=4=2\frac{r_{\text{He}}}{r_{\text{CH}_4}} = \sqrt{\frac{16}{4}} = \sqrt{4} = 2.
The rate of diffusion of a gas is inversely proportional to the square root of its molecular mass.

Anahtar Kavram

Graham's Law of Diffusion states that the rate of diffusion (rr) of a gas is inversely proportional to the square root of its molar mass (MM).
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