Question

Batteries are galvanic cells. What happens to E_cell as a battery discharge? Does a battery represent a system at equilibrium? Explain. What is E_cellwhen a battery reaches equilibrium? How are batteries and fuel cells a like? How are they different? The U.S. space program uses hydrogen-oxygen fuel cells to produce power for its space craft. What is a hydrogen-oxygen fuel cell?

Short answer

The cell potential starts decreasing to 0. A dead battery represents a system of equilibrium, E= 0. Batteries and fuel cells are both galvanic cells with potential and are useful. In a hydrogen-oxygen fuel cell, H and O are combined to generate electricity, heat, and water.

Step-by-step solution

Ecell after the battery discharges

Once a battery starts to discharge, its cell potential starts decreasing,and ultimately, it turns zero once the battery is dead.

System at equilibrium

A battery at equilibrium is a dead battery. At equilibrium, cell potential is zero and$\mathbf{∆}\mathbf{G}\mathbf{=}\mathbf{0}$. However, a battery reaches equilibrium, utilizing its potential is useful.

Difference and similarity between a fuel cell and a battery

Similarities between a fuel cell and a battery are:

• They both are galvanic cells.
• They both produce cell potential.
• They both are useful.

The difference is that fuel cells have reactants continuously supplied to them. They produce a current indefinitely, while this does not happen in the case of batteries.

Hydrogen-oxygen fuel cell

In a hydrogen-oxygen fuel cell, H and O are combined to generate electricity, heat, and water. The cell reaction of H-O fuel cell is:

$2{\mathrm{H}}_2\left(g\right)+{\mathrm{O}}_2\left(g\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(l\right)$

The two half-reactions are:

$$\begin{gathered} 4{\mathrm{e}}^{-}+{\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}\to 4{\mathrm{OH}}^{-}\left(cathode\right) \\ 2{\mathrm{H}}_2+4{\mathrm{OH}}^{-}\to 4{\mathrm{H}}_2\mathrm{O}+4{\mathrm{e}}^{-}\left(\mathrm{anode}\right) \end{gathered}$$