Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Energy, Exercise 8: Questions

Explain why lithium-ion batteries must be sealed.

Outline the function of the proton exchange membrane (PEM) in fuel cells. Explain why this membrane is important in microbial fuel cells?

A direct ethanol fuel cell has the following reactions:

Anode reaction: ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH} + 3{\mathrm{H}}_2\mathrm{O}\to 2{\mathrm{CO}}_2 + 12{\mathrm{H}}^{+} + 12{\mathrm{e}}^{-} {\mathrm{E}}^{⊝}=0.085 \mathrm{V}$

Cathode reaction: $3{\mathrm{O}}_2 + 12{\mathrm{H}}^{+}+ 12{\mathrm{e}}^{-} \to 6{\mathrm{H}}_2\mathrm{O} {\mathrm{E}}^{⊝} = 1.23 \mathrm{V}$

Overall reaction: ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH} + 3{\mathrm{O}}_2 \to 3{\mathrm{H}}_2\mathrm{O} +2{\mathrm{CO}}_2 {\mathrm{E}}^{⊝}=1.145 \mathrm{V}$

Calculate the theoretical thermal efficiency of this cell. The $∆{\mathrm{H}}^{⊝}$ value for the above reaction is $-1367 \mathrm{kJ}$.

In practice, ethanol fuel cells are less efficient than the direct methanol fuel cell, largely due to polarization and internal resistance. Ethanol has a larger energy density than methanol. Explain why this is an advantage and state two other advantages that a direct ethanol fuel cell might have over a direct methanol fuel cell.

Calculate the EMF of a concentration cell that has silver electrodes and $\left[{\mathrm{Ag}}^{+}\right] = 0.10 \mathrm{mol} {\mathrm{dm}}^{-3}$ in one cell and $2.0 \mathrm{mol} {\mathrm{dm}}^{-3}$ in the other. Which cell is the anode and which is the cathode?

Sketch an electrochemical cell that has $\mathrm{Zn}|{\mathrm{Zn}}^{2+}$ in one half-cell and $\mathrm{Al}|{\mathrm{Al}}^{3+}$ in the other, identifying the anode and cathode.

Use the given data and the Nernst equation to calculate the EMF of this cell if $\left[{\mathrm{Zn}}^{2+}\right] = 2.0 \mathrm{mol} {\mathrm{dm}}^{-3}$ and $\left[{\mathrm{Al}}^{3+}\right] = 0.50 \mathrm{mol} {\mathrm{dm}}^{-3}$.
$$\begin{gathered} {\mathrm{Al}}^{3+}\left(\mathrm{aq}\right)+ 3{\mathrm{e}}^{-} \to \mathrm{Al}\left(\mathrm{s}\right) {\mathrm{E}}^{⊝}=-1.66 \mathrm{V} \\ {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)+ 2{\mathrm{e}}^{-}\to \mathrm{Zn} \left(\mathrm{s}\right) {\mathrm{E}}^{⊝}=-0.76 \mathrm{V} \end{gathered}$$

List some advantages and disadvantages of hydrogen, direct methanol, and microbial fuel cells.