What is the overall reaction in an ethanol-oxygen fuel cell?

In an ethanol-oxygen fuel cell, the overall reaction involves the oxidation of ethanol (C2H5OH) in the presence of oxygen (O2) to produce carbon dioxide (CO2) and water (H2O). The balanced chemical equation for this process is:

C2H5OH + 3O2 → 2CO2 + 3H2O.

This equation accurately reflects the stoichiometry of the reaction, where one molecule of ethanol reacts with three molecules of oxygen, resulting in the production of two molecules of carbon dioxide and three molecules of water.

The balance of the equation is key; it shows how carbon atoms from ethanol are converted into carbon dioxide, and the hydrogen from ethanol is primarily found in the water produced. This reflects the underlying electrochemical processes occurring in the fuel cell, where electrons are transferred due to the oxidation of ethanol and the reduction of oxygen. The simplicity and conservation of mass in this equation conform to the principles of chemical reactions.

Other choices reflect incorrect stoichiometries or excessive ratios that do not accurately depict the balanced reaction that occurs in an ethanol-oxygen fuel cell. Therefore, option B is the correct overall reaction for this fuel cell system.