Differentiate between galvanic (voltaic) cells and electrolytic cells in terms of energy flow and external power source.

• A. Electrolytic cells require external power to drive a nonspontaneous reaction.
• B. Galvanic cells generate electrical energy spontaneously (Ecell > 0) from chemical energy; electrolytic cells require an external power source to drive a nonspontaneous reaction (Ecell < 0 under the applied conditions).
• C. Galvanic cells generate energy spontaneously; electrolytic cells do not exist.
• D. They operate in the same way.

Answer: (B)

The main idea is how energy moves between the chemical and electrical realms and when an external power source is needed. In a galvanic (voltaic) cell, a spontaneous redox reaction releases energy that is harnessed as electrical energy. The chemical energy drives electrons to flow through an external circuit from the anode to the cathode, producing an electric current and yielding a positive cell potential (Ecell > 0). Because the reaction would occur on its own, no outside power is required.

In contrast, an electrolytic cell drives a nonspontaneous reaction by applying an external power source. The outside energy forces electrons to move in a direction opposite to what the spontaneous reaction would dictate, so the external source supplies the energy to push the reaction forward. Under these applied conditions, the cell potential is effectively negative (Ecell < 0) unless the external power compensates, and the anode becomes positive while the cathode becomes negative due to the forced electron flow.

So the option that states galvanic cells generate energy spontaneously and electrolytic cells require an external power source to drive a nonspontaneous reaction captures both the direction of energy flow and the need for external power, making it the best description. The other choices either describe only one half of the picture, claim incorrect existence, or claim no difference in operation.