Look around. Have you ever stopped to wonder about things like why does iron rust? Why does your battery die? How do you get energy from food? All of these have to do with minute particles (electrons) that move from one atom to another. This particular action is what chemists refer to as movement as transfer electron reactions. For many of the chemical processes that happen in our daily lives, whether it is in metabolism, generation of electricity, reactions of electron transfer is the common daily answer.
In Chemistry, the Electron transfer reactions are the most important as they explain all the processes that happen when the atoms gain or lose electrons to create new products and give out energy.
This is a chemical reaction or process where electron(s) move from one to another substance. Because these two processes happen at the same time, they are also termed as redox processes.
When zinc combines with copper sulfate, the following reaction takes place:
Notice: Oxidation and reduction always occur together. One substance cannot be reduced unless another is oxidized.
An oxidation number is a number assigned to an atom that shows the charge it would have if the electrons were completely transferred.
For example, elements in the pure state have an oxidation number of 0.
Example: O₂, H₂, Fe (s) → 0
An ion that is monatomic (single atom) has an oxidation number equal to its charge.
Example: Na⁺ → +1, Cl⁻ → −1
Oxygen usually has an oxidation number of -2 and hydrogen has an oxidation number of +1. (There are exceptions)
Oxidation numbers are a deciding factor in determining which atom is oxidized and which is reduced.
An oxidizing agent is the substance that causes another to become oxidized. It gains electrons and is reduced in the process.
A reducing agent is the substance that causes another to be reduced. It loses electrons and is oxidized in the process.
H₂ is combined with O₂ to make water, shown by the following reaction:
When one substance is oxidized, and one is reduced, we refer to this as a redox reaction.
With redox reactions, we'll find it useful to write a separate half equation for each side.
Oxidation Half-Equation
This will show the loss of electrons:
Reduction Half-Equation
This will show the gain of electrons:
These half-partial equations will show which direction the electrons are moving, and when put together, serve to show the overall redox reaction.
Regular equations will show how to balance redox reactions, and the first difference you'll find is that you have to balance the electrons as you balance the various.
How to Do It
Example (acidic solution):
Reactions involving the loss of electrons happen everywhere:
Redox reactions explain the fundamentals of corrosion, energy storage, and industrial chemicals.
Redox reactions used to generate power produce electrochemical cells.
Key Terminology:
Each half reaction has a Standard Electrode Potential (E°) which reflects the tendency of a species to be reduced.
Example
Therefore, Cu²⁺ is reduced (strong oxidizing agent). Zn is oxidized (strong reducing agent).
E°cell calculation
This predicts whether the reaction will occur spontaneously.
Understanding electron transfer reactions is fundamental to chemistry and opens doors to countless practical applications.