3.6. Diffusion and Mass Transfer

Try these first

1. 1.

   What is the basic equation of diffusion discussed in this section?

   Hint

   Look for the relationship between concentration and diffusion in time.

2. 2.

   What does D represent in the diffusion equation?

   Hint

   Think about how quickly substances spread.

3. 3.

   What does the variable C represent in the diffusion equation?

   • Pressure
   • Concentration
   • Velocity

   Hint

   Remember the basic definition of concentration.

4. 4.

   True or False: The diffusion coefficient (D) is irrelevant in determining how quickly substances diffuse.

   • True
   • False

   Hint

   Think about how fast a substance spreads.

5. 5.

   Consider a body of water contaminated with a substance having a diffusion coefficient of 0.1 cm²/s. If the concentration at the source is 100 mg/L and in the surrounding water is 10 mg/L, estimate when the concentration will equalize within a distance of 10 cm. Use the diffusion equation appropriately.

   Hint

   Experiment with visualizing the diffusion process over time to assist in your calculation.

6. 6.

   A drug is released from a pill in a controlled manner with a diffusion coefficient of 2.0 x 10^-6 cm²/s. If it takes 2 hours for the drug concentration at a certain distance to reach 5 mg/L from an initial dose concentration of 200 mg/L, assess the effectiveness of the drug by evaluating diffusion parameters.

   Hint

   Focus on how releasing drugs slowly could result in consistent concentration levels that attain therapeutic goals.