Answer to Question #155547 in General Chemistry for ash

Question

1. Rank the gases Xe, CH4, F2, and CH2F2 in order of:
2. Increasing speed f effusion through a pinhole.
3. Increasing time of effusion.

Answer 1

• Effusion is the escape of gaseous molecules through a small hole into an evacuated space.
• The rate of effusion of a gaseous substance is inversely proportional to the square root of its molar mass (Graham's Law).
• Thus a lighter gas effuses through the same hole more rapidly than a heavier gas.
• The rank of increasing speed of effusion of gases will therefore be the rank of decreasing molecular weight of the gases.

Xe has molecular weight 131.293g/mol, CH₄ = 16.04g/mol, F₂ = 37.996g/mol, and CH₂F₂ = 52.024g/mol

The rank of increasing speed of effusion is therefore;

Xe < CH₂F₂ < F₂ < CH₄

Conversely, the time of effusion is inversely related to the rate, i.e. the faster the rate, the less the time of effusion. Hence, the rank of increasing time will be the opposite of the rank of increasing speed of effusion. Therefore;

CH₄ < F₂ < CH₂F₂ < Xe