Write cell reactions of hydrogen-oxygen fuel cell at anode and cathode.(b) Write an application of electrochemical series.

Answer:

(a) H₂–O₂ fuel cell with porous carbon electrodes and aqueous KOH (or NaOH) electrolyte:

Anode (oxidation): 2H₂(g) + 4OH^–(aq) → 4H₂O(l) + 4e^–

Cathode (reduction): O₂(g) + 2H₂O(l) + 4e^– → 4OH^–(aq)

Overall: 2H₂(g) + O₂(g) → 2H₂O(l)

(b) Application (any one): It helps predict whether a redox reaction is spontaneous: a metal with lower (more negative) standard reduction potential displaces a metal with higher reduction potential from its salt solution, e.g. Zn displaces Cu from CuSO₄. (It also compares the strengths of oxidising/reducing agents and helps calculate the standard emf of a cell, \(E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}\).)