Electrochemical cells — Chemistry, 14–17
Understand how a spontaneous redox reaction can drive electrons through a wire. Chemistry, 14–17 years.
Chemistry that makes a current
In a galvanic cell, oxidation releases electrons at one electrode and reduction accepts them at another. A wire gives the electrons a route, while ions move through a solution or salt bridge to keep charge balanced. The chemical reaction is therefore connected to a measurable voltage and current.
Why separate the reaction?
If a metal reacts directly with ions of another metal in the same mixture, electrons can pass straight through the liquid and much of the energy becomes heat. The problem is to control that electron transfer. Separating oxidation and reduction forces electrons through an external circuit, which is the basic idea behind a battery.
A zinc-copper cell
In a zinc-copper cell, zinc oxidises: Zn → Zn²⁺ + 2e⁻. Copper ions reduce: Cu²⁺ + 2e⁻ → Cu. Electrons travel from zinc to copper through the wire. Using standard potentials, E°cell = 0.34 − (−0.76) = 1.10 V, so the cell can drive a current while both half-cells remain connected ionically.
Anode and cathode
Many people memorise that the anode is negative and the cathode positive, because that is true for a galvanic cell. The safer rule is chemical: oxidation always happens at the anode and reduction at the cathode. In an electrolytic cell the signs swap, but these reaction names do not.
Batteries and corrosion
Portable batteries use separated redox reactions to power phones, clocks and vehicles. The same chemistry can cause corrosion when two different metals and a conducting liquid make an unwanted cell. Engineers use coatings, sacrificial metals and circuit design to control where oxidation happens.
Keep exploring
Other languages
Loading MyLeoNes™…