Intro to redox reactions

[Bri MT]

In redox reactions there’s always both reduction and oxidation.

Oxidation: loss of electrons; the process that happens to the reducing agent
Reduction: gain of electrons; the process that happens to the oxidation agent
(yes, the terminology is confusing  )
This is shown in the acronym OILRIG:
Oxidation Is Loss  (OIL)
Reduction Is Gain  (RIG)

Some species like being transferred electrons a lot than others (strong oxidising agents) whereas some like accepting electrons a lot (strong reducing agents). What redox reactions will occur (if any) is determined by the strength of the species present as oxidising and reducing agents. To check this we look at the series in the data book. The left side of the reversible arrows has oxidising agents while the right hand side has reducing agents. The further down a species is on the list the stronger it is as an oxidising agent and the weaker it is as a reducing agent.
If a reaction occurs, it will be between the strongest oxidising agent present and the strongest reducing agent present. To see if this reaction occurs spontaneously, you need to take the standard electrode potential (show on the right of the series) of the reduction reaction and subtract the standard electrode potential of the oxidation reaction. If the result is greater that zero the reaction will occur spontaneously. Another trick to see the directional of a line drawn between the reactants. If the line goes / the reaction is spontaneous and if the line goes \ the reaction is non-spontaneous.

Note: redox reactions occur in electrochemical cells but also in other places as well. For example, the reaction that produces rust is a redox reaction where iron is oxidised.

[^^^111^^^]

In redox reactions there’s always both reduction and oxidation.

Oxidation: loss of electrons; the process that happens to the reducing agent
Reduction: gain of electrons; the process that happens to the oxidation agent
(yes, the terminology is confusing  )
This is shown in the acronym OILRIG:
Oxidation Is Loss  (OIL)
Reduction Is Gain  (RIG)

Some species like being transferred electrons a lot than others (strong oxidising agents) whereas some like accepting electrons a lot (strong reducing agents). What redox reactions will occur (if any) is determined by the strength of the species present as oxidising and reducing agents. To check this we look at the series in the data book. The left side of the reversible arrows has oxidising agents while the right hand side has reducing agents. The further down a species is on the list the stronger it is as an oxidising agent and the weaker it is as a reducing agent.
If a reaction occurs, it will be between the strongest oxidising agent present and the strongest reducing agent present. To see if this reaction occurs spontaneously, you need to take the standard electrode potential (show on the right of the series) of the reduction reaction and subtract the standard electrode potential of the oxidation reaction. If the result is greater that zero the reaction will occur spontaneously. Another trick to see the directional of a line drawn between the reactants. If the line goes / the reaction is spontaneous and if the line goes \ the reaction is non-spontaneous.

Note: redox reactions occur in electrochemical cells but also in other places as well. For example, the reaction that produces rust is a redox reaction where iron is oxidised.

Thank you for making this I just have a doubt - what exactly are oxidation numbers , and is there a way of remembering the oxidation numbers of all elements?

[Bri MT]

Thank you for making this I just have a doubt - what exactly are oxidation numbers , and is there a way of remembering the oxidation numbers of all elements?

No worries! Oxidation numbers are a bit hard to define - I think of them as being similar to charge & describing the excess/deficit of electrons situation that a species is in (they aren't the same as charge so definitely don't write that they are). If a species is reduced than its oxidation number is reduced & if a species is oxidised than its oxidation number is increased.

For finding oxidation numbers you want to remember these rules:
-   The oxidation number of an element is zero
-   The oxidation number of a compound is the sum of the oxidation numbers of the atoms
-   The oxidation number of a transition metal is equal to its charge
-   The oxidation number of hydrogen in a compound is +1 unless it’s in a hydride in which case it’s -1
-   The oxidation number of oxygen in a compound is -2 unless it’s in a peroxide in which case it’s -1 or in OF2 in which case it’s +2
-   The oxidation number of fluorine in a compound is always -1

For example, in H2O oxygen has an oxidation number of -2  and each hydrogen atom has an oxidation number of +1. 2*(+1) + 1*(-2) = 0, which is the answer we need to get since H2O has no overall charge.