what is mean by redox reaction?

 the reaction in which oxident is reduced by accepting electrons and reductant is oxidised by losing electrons is known as redox reaction

When the reacting species, capable of losing electrons (reducing agent) and that capable of gaining electrons (oxidizing agent) are present in the same solution a direct redox reaction takes place. In direct redox reactions, the electrons move randomly in all the directions through very short distances. So, in direct redox reactions the net movement of electrons in any direction is zero. The change in chemical energy in such reactions appears as heat.
For example, Oxidation of Zn by Cu²⁺_.

When a strip of metallic zinc is placed in a solution of CuSO₄, after sometime it is noticed that,

• A part of zinc metal plate has dissolved and has lost weight.

• The bluish colour of the solution gradually fades away.

• Reddish metallic copper has started depositing on the zinc plate or is settling down at the bottom of the beaker.

• The presence of Zn²⁺ ion in the solution may be confirmed by passing H₂S gas through the colourless solution after making it ammoniacal by adding ammonia and ammonium chloride when white precipitate of ZnS (zinc sulphide) is formed. The solution remains electrically neutral during and after the reaction.

These observations can be explained as follows:

Solution of copper sulphate contains Cu²⁺_(aq) and SO₄^2-_(aq) ions. When zinc plate is placed in a solution of copper sulphate, zinc being more electropositive than copper, loses electrons to form Zn²⁺ions. The Cu²⁺ ions gain these electrons to form copper metal. This is displaced as copper metal, a reddish precipitate. As the concentration of Cu²⁺ ions present in the copper sulphate solution decreases the blue colour of the solution fades away. The overall reaction may be written as:

Electrons are transferred from Zn atom to Cu²⁺ ion directly. So, this reaction is a direct redox reaction.

Fig: - Displacement of copper from copper sulphate solution by zinc

Redox (reduction-oxidation) reactions include all chemical reactions in which atoms have their oxidation state changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO₂) or the reduction of carbon by hydrogen to yield methane (CH₄), or a complex process such as the oxidation of glucose (C₆H₁₂O₆) in the human body through a series of complex electron transfer processes.

Fundamentally, redox reactions are a family of reactions that are concerned with the transfer of electrons between species. The term comes from the two concepts of reduction and oxidation.^[1] It can be explained in simple terms:

• Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.
• Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.

Although oxidation reactions are commonly associated with the formation of oxides from oxygen molecules, these are only specific examples of a more general concept of reactions involving electron transfer.

Redox reactions, or oxidation-reduction reactions, have a number of similarities to acid-base reactions. Like acid-base reactions, redox reactions are a matched set, that is, there cannot be an oxidation reaction without a reduction reaction happening simultaneously. The oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction. When writing half-reactions, the gained or lost electrons are typically included explicitly in order that the half-reaction be balanced with respect to electric charge.

what is double decompotion reacation??

prepretion of hydrogen