Why does the anode carry negative charge in galvanic cell but positive
charge in electrolytic cell?
The Correct Answer and Explanation is :
In electrochemistry, the difference in charge at the anode in galvanic (or voltaic) and electrolytic cells is due to the direction of electron flow and the type of reactions occurring at each electrode. Here’s an explanation:
- Galvanic Cell (Voltaic Cell):
In a galvanic cell, the anode carries a negative charge. This is because a galvanic cell is designed to generate electrical energy from spontaneous redox reactions. At the anode, oxidation occurs, meaning electrons are released by the substance being oxidized. These electrons accumulate on the anode, making it negatively charged. The electrons then flow through the external circuit to the cathode, where reduction takes place. Thus, the anode in a galvanic cell is negative, as it supplies electrons to the circuit. - Electrolytic Cell:
In an electrolytic cell, the anode is positively charged. This cell type uses an external power source to drive a non-spontaneous reaction, essentially forcing electrons to flow in the opposite direction of a galvanic cell. Here, oxidation still occurs at the anode, but the power source pulls electrons away from it, creating a deficiency of electrons and thus a positive charge. The anode attracts anions from the electrolyte to facilitate oxidation reactions. In this setup, the external power source drives electrons toward the cathode, where reduction occurs. - Key Differences Explained:
- In both cells, oxidation happens at the anode and reduction at the cathode, but the charge on the anode differs due to electron movement and the nature of the reactions.
- The galvanic cell’s anode is negative because it produces electrons from spontaneous oxidation.
- The electrolytic cell’s anode is positive because the external power source pulls electrons away, forcing non-spontaneous oxidation.
In summary, the anode in a galvanic cell is negative because it releases electrons spontaneously, while in an electrolytic cell, it’s positive as the power source draws electrons away, driving a reaction that wouldn’t occur on its own.