Redox Reactions

You have likely seen a sliced apple turn brown on the kitchen counter or an outdoor bicycle chain gather reddish rust after a rainstorm. From spoiled food to a roaring campfire, all of these everyday occurrences are redox reactions at work.

Early scientists originally coined the term 'oxidation' to describe substances gaining oxygen. It was an intuitive name because they observed apple flesh or bare iron combining with oxygen in the air and changing in appearance. Conversely, losing oxygen and returning to a pure elemental state was called 'reduction.'

Smelting plants have used this principle for centuries to extract iron from mined ore. Natural iron ore is tightly bonded with oxygen. Stripping that oxygen away to restore strong, shiny elemental iron is a classic real-world example of reduction.

Many chemical reactions show the exact same behavior even when there is no oxygen around at all. This prompted scientists to uncover a deeper, universal rule. As it turns out, the real driving force behind oxidation and reduction is electrons hopping between atoms.

In modern chemistry, losing electrons is defined as oxidation, while gaining electrons is defined as reduction. Because electrons carry a negative (-) charge, picking up extra electrons actually reduces an atom's overall charge, or oxidation state. The term 'reduction' originally came from reducing ore down to metal, but it neatly matches the fact that the charge decreases.

Electrons cannot simply wander off into thin air. If one substance releases electrons, another must take them up immediately. Just like handing cash across a counter requires both a giver and a receiver, oxidation and reduction always happen as a synchronized pair.

Redox reactions do far more than rust metal or rot fruit. In fact, they are the very engine that powers our bodies when we breathe and convert food into fuel.

Inside our cells, glucose from the food we eat is gradually oxidized with oxygen, safely releasing the biological energy needed to move, think, and maintain body heat. In plant photosynthesis, the opposite occurs: water is oxidized to release oxygen gas, and those electrons reduce carbon dioxide into glucose.

Redox also powers the batteries inside smartphones and electric vehicles. Whether charging or discharging, oxidation and reduction take place simultaneously at opposite electrodes. When you plug your phone into a wall charger, you simply drive those same reactions backward.