5.26C - Hydrogen-oxygen fuel cells
A hydrogen-oxygen fuel cell uses a continuing supply of gases to provide electrical energy. You will connect its reactants, water product and electrical output, and distinguish it from burning a fuel.
Reactants, product and energy transfer
A hydrogen-oxygen fuel cell uses hydrogen and oxygen to produce a voltage. With a complete circuit connected, it supplies a current and transfers energy electrically. Water is its only chemical product; some energy is also transferred to the surroundings as heat. Heat and voltage are not chemical substances.
The equation conserves atoms: four hydrogen atoms and two oxygen atoms appear on each side. Hydrogen and oxygen are the reactants; water is the product. Carbon dioxide cannot be formed from these pure reactants because neither contains carbon.
The cell converts chemical energy directly into electrical energy through reactions at electrodes. It does not burn hydrogen in a flame to run a generator. Burning hydrogen also produces water, but initially transfers energy by heating; observing water alone does not identify a fuel cell.
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