Electrochemical cells – Primary vs. secondary sources: A secondary cell produces direct current via chemical reactions; a primary cell generates direct current by which process?

Introduction / Context:
Both primary and secondary cells are galvanic devices that convert chemical energy into electrical energy. The key difference lies in reversibility: secondary cells are rechargeable, while primary cells are intended for single-use discharge.

Given Data / Assumptions:

• The statement already notes that a secondary cell generates DC through chemistry.
• We compare the mechanism of primary cells to confirm it is the same fundamental process.

Concept / Approach:
Primary cells (zinc–carbon, alkaline) and secondary cells (lead–acid, nickel–metal hydride, lithium-ion during discharge) both generate electromotive force due to spontaneous redox reactions at their electrodes. In primary cells, the reactions are not designed to be efficiently reversible; in secondary cells, charging reverses the chemistry.

Step-by-Step Solution:
Identify the source of EMF in galvanic cells: redox chemistry.Recognize that both primary and secondary cells use chemical reactions to produce DC.Select the option that states chemically.

Verification / Alternative check:
Observe that no purely electrical process inside a passive cell can sustain DC output without a chemical or physical energy source; heat or light can drive separate devices (thermopiles, photovoltaics) but those are not primary batteries.

Why Other Options Are Wrong:

• Electrically: electricity is the output, not the internal energy source.
• Thermally: thermoelectric devices differ from chemical cells.
• Optically: photovoltaic cells produce DC from light, not considered primary chemical cells.
• Mechanically: generators convert mechanical to electrical energy, not battery operation.

Common Pitfalls:
Confusing the discharge mechanism with the recharge mechanism; only secondary cells accept electrical energy to reverse chemistry during charging.

Final Answer:
Chemically