Question

Fick's first law of diffusion states that the rate of mass transfer is proportional to the:

• A. Concentration
• B. Pressure difference
• C. Concentration gradient
• D. Temperature gradient

Hint:

Logic Tip: Just like a steep hill (elevation gradient) makes a ball roll faster, and a sharp temperature difference (temperature gradient) makes heat flow faster, a sharp difference in concentration (concentration gradient) drives mass to diffuse faster.

Answer 1

The Correct Option is C

Concept:
Mass transfer by molecular diffusion is governed by Fick's First Law, which is analogous to Fourier's law for heat conduction and Newton's law for momentum transfer.

Step 1: Fick's first law in one dimension is expressed as: $J_A = -D_{AB} \frac{dC_A}{dz}$.

Step 2: In this equation, $J_A$ is the molar flux (rate of mass transfer per unit area), $D_{AB}$ is the diffusion coefficient (diffusivity), $C_A$ is the concentration of species A, and $z$ is the distance.

Step 3: The term $\frac{dC_A}{dz}$ represents how the concentration changes over a specific distance. This spatial change in concentration is called the "concentration gradient".

Step 4: The equation explicitly shows that the rate of mass transfer ($J_A$) scales directly with the steepness of this concentration gradient.