0.0008
mol/(m²·s)
0.000008
mol/s
8
mol/m³
800,000
mol/m⁴
0.0008
mol/(m²·s)
0.000008
mol/s
8
mol/m³
800,000
mol/m⁴
The Diffusion Rate Calculator uses Fick's First Law to determine the flux of a substance across a membrane or barrier. Diffusion is the net movement of molecules from a region of higher concentration to lower concentration, driven by the concentration gradient. This process is essential in biology for gas exchange in lungs, nutrient absorption in the gut, and neurotransmitter signaling.
Fick's Law quantifies this process, relating the rate of diffusion to the diffusion coefficient of the substance, the concentration difference, and the thickness of the barrier.
Fick's First Law of diffusion states:
J = -D × (C₁ - C₂) / Δx
The negative sign indicates diffusion occurs down the gradient. This calculator reports the magnitude of the flux (absolute value). A steeper gradient or thinner membrane increases the diffusion rate.
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Oxygen diffuses rapidly across the thin (1 µm) alveolar membrane due to a large concentration gradient and thin barrier.
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Glucose diffuses more slowly due to its larger size (lower D) and thicker barrier, illustrating why cells use facilitated transport.
The diffusion coefficient (D) measures how quickly a substance diffuses through a medium. It depends on molecular size, medium viscosity, and temperature. Smaller molecules in less viscous media at higher temperatures have larger D values. For example, oxygen in water has D of about 2.1 × 10⁻⁹ m²/s at 25°C.
Fick's Law explains how gases, nutrients, and waste products move across biological membranes. It underlies gas exchange in the lungs, nutrient absorption in the intestines, kidney filtration, and the design of drug delivery systems. Understanding these rates helps predict biological efficiency.
Fick's First Law assumes steady-state conditions (constant gradient), a homogeneous medium, and passive diffusion only. In biological systems, membranes are heterogeneous, gradients change over time, and active transport can work against the gradient. For time-dependent diffusion, Fick's Second Law is needed.
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