puolireaktion

Puolireaktio, also known as a half-reaction, is a term used in chemistry to describe either the oxidation or reduction part of a redox reaction. Redox reactions involve the transfer of electrons between chemical species. A complete redox reaction can be conceptually divided into two half-reactions: one where a species loses electrons (oxidation) and another where a species gains electrons (reduction).

For example, in the reaction between zinc metal and copper(II) ions, zinc is oxidized to zinc ions (Zn -> Zn2+ + 2e-), and copper(II) ions are reduced to copper metal (Cu2+ + 2e- -> Cu). These two separate equations represent the oxidation half-reaction and the reduction half-reaction, respectively. When combined, they form the overall redox reaction: Zn + Cu2+ -> Zn2+ + Cu.

Half-reactions are crucial for understanding the mechanisms of electrochemical cells, such as batteries and electrolytic cells. By analyzing the individual half-reactions, chemists can determine the standard electrode potentials, predict the direction of electron flow, and calculate the cell voltage. The concept of half-reactions also helps in balancing complex redox equations, ensuring that the number of electrons lost in oxidation equals the number gained in reduction. This fundamental concept is a cornerstone of electrochemistry and chemical kinetics.