What is the overall chemical reaction in a hydrogen fuel cell?

• A. 2H2 + O2 → 2H2O + electricity + heat
• B. 2H2O → 2H2 + O2
• C. H2 + O2 → H2O2
• D. H2 + O2 → H2O

Answer: (A)

Hydrogen fuel cells turn the chemical energy of hydrogen and oxygen directly into electrical energy, with water as the main chemical product. The core reaction is 2 H2 + O2 → 2 H2O, which releases energy. In a functioning cell, that energy is captured as electricity flowing through an external circuit, and some is released as heat due to inefficiencies. So describing the overall process as 2 H2 + O2 → 2 H2O + electricity + heat reflects both the chemical change and the practical energy output you get from the cell. The reverse reaction or forming hydrogen peroxide would not describe how a fuel cell operates, and simply writing the chemical equation without mentioning energy output misses the key way a fuel cell provides power.