why is it necessary for oxidation and reduction reactions to occur as paired reactions?

Question

why is it necessary for oxidation and reduction reactions to occur as paired reactions?

I don't understand this. :S Grr

Answer 1

Think of what occurs in a Reduction-Oxidation (Red-Ox) reaction....One substance is reduced and another substance is oxidized.
LEO - GER
Loose Electrons Oxidization
Gain Electrons Reduction

When something is reduced it gains electrons...but from where? These electrons didn’t just come out of thin air, there are not that many free electrons floating around normally, so some other substance must have provided them...the substance which is oxidized. When something is oxidized it looses electrons and these electrons go off to reduce another substance.

Spontaneous Reduction - Oxidation reactions only occur when there is a negative change in the Gibbs free energy (this is what makes it spontaneous). In other words, two substances, in general, will not reduce/oxidize each other unless it is energetically favorable to do so....if the substances will be "happier" with/without these extra electrons.
For example, Lithium metal (Li) has only 1 electron in its outermost S orbital, if it could loose this electron it could obtain a Noble gas configuration (like He) and become much more stable. On the other hand, Fluorine has an almost filled valence shell, it needs just one more to be complete and have a Noble ga configuration. Lithium would REALLY like to loose that extra electron and Fluorine would REALLY like to gain an extra electron. When put together Lithium will be oxidized by Fluorine and Fluorine will be reduced by Lithium at the same time.
Li --> Li+ + e-
F2 + 2e- --> 2F-
Since Fluorine is diatomic, for every 1 molecule of Fluorine, there are 2 atoms of Fluorine and each atom needs 1 extra electron. For this reason, the Lithium oxidation reaction must occur twice as fast as the Fluorine reduction reaction, but the two still must occur together.
2Li + F2 --> 2LiF
In this way both the mass of the substances and the charge is balanced in the chemical reaction.

Answer 2

It has to do with the first law of thermodynamics. In a chemical reaction, nothing is created or destroyed, substances just change conformations. In order for there to be a reduction, a gain of an electron, there must also be an oxidation, a loss of an electron. If substance A gain an electron, that electron must come from something else. Another substance, B, must be losing an electron or A would have nothing to gain.

Answer 3

No no longer all reaction are redox. reaction between metals and non-metals are purely redox reaction Redox ability alleviation and oxidation, that's the earnings or loss of electron forming and ionic bond. Oxidation=loss of electrons alleviation= earnings of electrons e.g.a rection between a nonmetal and steel is straightforward as redox reaction. Metals are oxidized Non-metasl are decreased there is exchange in oxidation state. even with the undeniable fact that in the process non-metals there's a covalent bonding, electrons are no longer gained or lost yet rather is shared. that's no longer a redox reaction. keep in mind : Redox could contain metals. Metals are resposible for any redox reaction

Answer 4

Because when one molecule loses an electron another molecule gains an electron. Electrons have to go some where.
For an example.
pyruvate +NADH +H -----------> lactic acid +NAD+

pyruvate ----------------------> lactic acid (reduction)
NADH+H ---------------> NAD+ (oxidation)

Pyruvate gains electrons to become lactic acid
NADH+ H loses an electron to be come NAD+