Fick's law describes a concept called flux. Flux is the rate at which something accumulates or dissipates. It is measured in units of volume per unit of time per unit area. Suppose you had a bathtub with a drain one inch by one inch square. You add one gallon of water to the tub and then opened the drain. If it takes 1 minute to empty 1 gallon of water through the drain, then the flux of water is one gallon per minute, per square inch of drain. Fick's First Law: J = -D(dc/dx), where c in concentration and x is distance Determine the rate of diffusion (flux) in mol/s-cm2 for aspirin dissolving through the stomach lining given the concentration at the blood vessel is C1= 5 mg/L and in the stomach is C2 = 105 mg/L. The diffusivity constant of aspirin is 0.09 x 10-6 mm2/s and the thickness of the stomach lining is approximately 0.4 cm. Be sure to define c1 and x1 so the response makes sense. A drawing often helps explain it well.