Week 10

Question 1

What is convection time?

Answer 1

The time taken for a molecule to be transported by
convection.

Question 2

What is diffusion time?

Answer 2

The time taken for a molecule to be transported by
diffusion.

Question 3

What does a large Peclet number indicate?

Answer 3

Dominant convection transport
over diffusion.

Question 4

What is a dilute solution in terms of concentrations?

Answer 4

𝐶s&raquo_space; Ci

(𝐶s is the solvent concentration)

Question 5

What is the dilute assumption?

Answer 5

Mass average velocity will equal molar average
velocity, both will be approx equal to solvent velocity.

Solute-solute interaction no longer important, treat a multicomponent transport as if the mixture were
binary.

Question 6

What is the need of the partition coefficient?

Answer 6

Concentration need not be continuous
across an interface.

Question 7

In the random walk model, if the mean displacement is 0, how does diffusion occur?

Answer 7

Mean the spread is not 0. The region of space sampled by the diffusing molecules grows with time, symmetrically.

Question 8

Why is the mean displacement 0 in random walk model?

Answer 8

Since a particle is
equally likely to jump forward or backward, summation of ±𝛿 will
be zero.