Which device spontaneously generates electricity from chemical reactions?

• A. Electrolytic cell
• B. Fuel cell
• C. Battery
• D. Galvanic cell

Answer: (D)

Spontaneous redox reactions release chemical energy that can be turned into electrical energy, and that's exactly what a galvanic cell does. In this setup, oxidation happens at the anode and reduction at the cathode, with electrons flowing through an external circuit from the anode to the cathode. Because the overall reaction has a positive cell potential, the process is thermodynamically favorable (the Gibbs free energy change is negative), so electricity is produced without an outside energy source. A familiar example is the Daniell cell, where zinc is oxidized and copper ions are reduced, driving a current as long as reactants remain.

An electrolytic cell, by contrast, requires external electrical energy to push a non-spontaneous reaction. A fuel cell does generate electricity from a chemical reaction between a fuel and an oxidant, but it relies on a continuous supply of reactants. A battery is a general term for devices that store chemical energy; a galvanic cell is the type that spontaneously converts that stored chemical energy into electrical energy.