What is spontaneous redox reaction?

Hint: A spontaneous redox reaction may be a sort of reaction during which there's usually the discharge of energy where the electrons are transferred from let’s say anode to cathode. This sort of reaction is usually seen in electrochemical cells. Here, the reaction results in the generation of electricity.

Complete answer:
In redox reactions, electrons are being transferred from one species to a different, spontaneous means energy is being released and it can then be wont to work. The work that you simply are pertaining to may be the separate half-reactions, oxidation, and reduction reactions.
When these are put in separate containers and electrons are being transferred from anode to cathode (in other words doing work), and within the process creating an electrochemical gradient that's generating electricity, which is why the voltage changes.
In 1793, Alessandro Volta discovered that electricity might be produced by placing different metals on the other sides of a wet paper or cloth. He made his first battery by placing Ag and Zn on the other sides of a moistened cloth with salt or weak acid Solution. Therefore, these batteries acquired the name voltaic cells.
Voltaic (galvanic) cells are electrochemical cells that contain a spontaneous reaction, and always have a positive voltage. The electricity released during the reaction often wants to work. A galvanic cell consists of two compartments called half-cells.

Note:
Oxidation is the loss of electrons, whereas reduction refers to the acquisition of electrons, as illustrated within the respective reactions above. The species being oxidized is additionally referred to as the reducer or reductant, and therefore the species being reduced is named the oxidant or oxidant.