In steady-state molecular diffusion of gas A through a stationary gas B, the ratio NA/(NA + NB) equals____________________?
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Answer: A. 1
Explanation
Gas B is stationary meaning its molar flux is zero during steady-state molecular diffusion. Substituting zero for the flux of gas B simplifies the mathematical ratio to exactly one. The ratio numerator and denominator become identical when the stagnant gas flux vanishes completely. Molecular diffusion describes mass transport driven by concentration gradients across a system boundary. Stagnant film theory assumes one component diffuses through a stationary fluid barrier. Ficks law governs the fundamental rate of molecular mass transfer in binary mixtures.
This specific diffusion model applies directly to Stefan tube experiments in laboratories. Evaporation of liquid droplets into a stagnant gas envelope follows this exact principle. Chemical engineers use this ratio to calculate mass transfer coefficients for porous catalysts. An infinity value occurs exclusively during equimolar counter-diffusion when fluxes cancel out. A value of zero would imply that the diffusing species has no active mass flux. Intermediate numerical values like zero point five represent different relative molar flux conditions.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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