3. Thermodynamics and Phases

Diffusion — Quiz

Test your understanding of diffusion with 5 practice questions.

Practice Questions

Question 1

Given a thin palladium sheet of thickness $0.5\,\mathrm{mm}$ with surface concentrations $C_A=2.0\,\mathrm{kg/m^3}$ and $C_B=0.4\,\mathrm{kg/m^3}$, and diffusion coefficient $D=1.0\times10^{-8}\,\mathrm{m^2/s}$, what is the steady-state diffusion flux $J$?

Question 2

If the diffusion flux $J$ has units $\mathrm{kg/(m^2\cdot s)}$ and the concentration gradient $dC/dx$ has units $\mathrm{kg/m^4}$, what are the SI units of the diffusion coefficient $D$ according to Fick’s First Law $J=-D\,dC/dx$?

Question 3

In substitutional diffusion in metals, which mechanism is primarily responsible for atomic motion?

Question 4

For non-steady-state diffusion into a semi-infinite solid, the depth $x$ at which a given concentration is reached scales with time $t$ as $x\propto\sqrt{Dt}$. If a desired concentration occurs at $x=2\,\mathrm{mm}$ after $10$ hours, how long will it take to reach the same concentration at $x=6\,\mathrm{mm}$?

Question 5

In the Arrhenius-type expression $D=D_0\exp\bigl(-Q_d/(RT)\bigr)$ for the diffusion coefficient, what does $Q_d$ represent?