The Electromotive Force (EMF) is the potential difference that drives current in a galvanic cell, whereas a galvanic cell is the entire electrochemical system that produces electrical energy through spontaneous redox reactions.
Here's a breakdown of the differences:
EMF (Electromotive Force)
- Definition: EMF is the potential difference between the two electrodes (anode and cathode) in a cell when no current is flowing (open circuit condition). It's essentially the "driving force" or voltage that pushes electrons through the external circuit. It is measured in volts (V).
- Measurement: It represents the maximum possible voltage that a cell can deliver. This maximum voltage occurs when the cell isn't doing any work (i.e., not supplying current).
- Source: It arises from the difference in the electrochemical potentials of the two half-cells (oxidation and reduction half-reactions) that make up the galvanic cell.
- Calculation: EMF can be calculated using the standard reduction potentials of the half-reactions: E°cell = E°cathode - E°anode
- Relationship to Galvanic Cells: The EMF is a property of a galvanic cell. It characterizes the cell's ability to produce voltage.
Galvanic Cell (Voltaic Cell)
- Definition: A galvanic cell (also known as a voltaic cell) is an electrochemical cell that uses spontaneous redox reactions to generate electrical energy. It converts chemical energy into electrical energy.
- Components: A galvanic cell consists of two half-cells: an anode (where oxidation occurs) and a cathode (where reduction occurs), connected by an external circuit to allow electron flow and a salt bridge (or porous barrier) to maintain electrical neutrality.
- Function: A galvanic cell allows the spontaneous electron transfer in a redox reaction to be harnessed to do electrical work.
- Process: At the anode, a metal loses electrons and dissolves into the solution (oxidation). These electrons flow through the external circuit to the cathode, where ions in the solution gain electrons and deposit as a metal (reduction).
- Examples: Common examples of galvanic cells include batteries (like alkaline batteries, lead-acid batteries in cars), and fuel cells.
Summary Table
| Feature | EMF (Electromotive Force) | Galvanic Cell (Voltaic Cell) |
|---|---|---|
| Definition | Potential difference, driving force for current. | Electrochemical system that produces electrical energy. |
| Nature | A measurement (voltage). | A physical device (system). |
| Function | Drives electron flow in the external circuit. | Converts chemical energy into electrical energy through redox reactions. |
| Components | N/A (It is a property, not a structure.) | Anode, cathode, electrolyte(s), external circuit, salt bridge/porous barrier. |
| Occurrence | Present in a galvanic cell (and other circuits). | Exists as a complete electrochemical setup. |
In essence, think of a galvanic cell as a car, and the EMF as the potential energy in the gasoline that allows the car to move. The galvanic cell is the whole setup, while the EMF drives the process.
