Chemistry · Electrochemistry · NEET
| Energy change | Chemical energy to electrical energy | Electrical energy to chemical energy |
| Reaction type | Spontaneous (runs by itself) | Non-spontaneous (needs a push) |
| E°cell sign | Positive (+) | Negative (needs external EMF) |
| ΔG° | Negative | Positive |
| Anode sign | Negative (−) | Positive (+) |
| Cathode sign | Positive (+) | Negative (−) |
| Example | Daniell cell, dry cell | Electrolysis of molten NaCl, electroplating |
A galvanic (voltaic) cell runs on a reaction that happens by itself (spontaneous), so it produces electricity. An electrolytic cell uses an external battery to push a reaction that would not happen on its own (non-spontaneous). So one gives energy out, the other takes energy in. This is the single idea NEET tests most, so lock it first.
A galvanic cell is spontaneous. Its cell reaction has a positive E°cell and a negative ΔG°, which are the math signals of a spontaneous process. An electrolytic cell is non-spontaneous: left alone nothing happens, so you must supply an external EMF larger than the reverse voltage to make it run.
In a galvanic cell the anode is the negative electrode and the cathode is positive (electrons leave from anode into the wire). In an electrolytic cell it flips: the anode is positive and the cathode is negative, because the external battery's + terminal pulls electrons and defines the signs. One rule never changes though: oxidation always happens at the anode, reduction always at the cathode, in BOTH cells.
The galvanic cell has a positive E°cell, because its reaction is spontaneous. If a proposed cell gives a negative E°cell, the reaction will not run by itself; to force it you build an electrolytic cell and supply an external voltage. NTA loves the sign link: +E°cell means galvanic/spontaneous, −E°cell means you need electrolysis.
Galvanic cell: chemical energy is changed into electrical energy (it acts like a battery you can use). Electrolytic cell: electrical energy from a battery is changed into chemical energy (it splits or deposits substances). Simple line for the exam: galvanic makes current, electrolytic uses current.
Yes. The definitions never change: the electrode where oxidation happens is the anode, and the electrode where reduction happens is the cathode, in every electrochemical cell. Only the + / − signs of these electrodes swap between the two cell types. Students lose easy marks by mixing up sign with the oxidation/reduction rule, so keep them separate.
If the E°cell for a given reaction has a negative value, which of the following gives the correct relationships for the values of ΔG° and Keq?
During the electrolysis of molten sodium chloride, the time required to produce 0.10 mol of chlorine gas using a current of 3 amperes is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The Daniell cell is a galvanic cell. Zinc metal spontaneously gives electrons to copper ions, producing electricity with a positive E°cell of about +1.10 V. No external battery is needed.
Yes, in principle. If you connect an external battery larger than a galvanic cell's own EMF and in the opposite direction, you force the reverse reaction, turning it into an electrolytic cell. This is how rechargeable batteries work: discharging is galvanic, charging is electrolytic.
Oxidation always happens at the anode in both galvanic and electrolytic cells. Only the electrical sign of the anode changes: negative in a galvanic cell, positive in an electrolytic cell.
In a galvanic cell electrons are produced at the anode and pushed out, making it negative. In an electrolytic cell the external battery's positive terminal is joined to the anode and pulls electrons out, making it positive. The battery decides the signs.
The electrolytic cell converts electrical energy into chemical energy, for example depositing copper or splitting molten NaCl. The galvanic cell does the reverse, converting chemical energy into electrical energy.
