Question

According to Fick's First Law, the molecular diffusion flux depends on:

• A. Difference in Temperature
• B. Pressure Difference
• C. Concentration Gradient
• D. Difference in Concentration

Hint:

Flux is always driven by a Gradient. Just as heat flux depends on a *Temperature Gradient* (Fourier's Law), mass flux depends on a *Concentration Gradient*.

Answer 1

The Correct Option is C

Concept: Fick's First Law describes the relationship between the diffusion flux and the concentration distribution of a substance under steady-state conditions.

Step 1: The Mathematical Form of Fick's Law.
The law is stated as: \[ J = -D \frac{dc}{dx} \] Where:
• \( J \) = Diffusion flux (\( mol/m^2 \cdot s \)).
• \( D \) = Diffusion coefficient or diffusivity (\( m^2/s \)).
• \( \frac{dc}{dx} \) = Concentration Gradient.

Step 2: Distinguishing "Gradient" from "Difference".
While a concentration "difference" exists between two points, the "gradient" is the spatial rate of change (difference divided by distance). Fick's law specifically states that the flux is proportional to this spatial gradient. The negative sign indicates that diffusion occurs from high concentration to low concentration.