what are redox reaction? Explain with equation mention two characteristics of chemical reaction with experiments. (6 marks)
Answers
Redox (short for reduction–oxidation reaction) (pronunciation: /ˈrɛdɒks/ redoks or /ˈriːdɒks/ reedoks[1]) is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a reduction process and a complementary oxidation process, two key concepts involved with electron transfer processes.[2] Redox reactions include all chemical reactions in which atoms have their oxidation state changed; in general, redox reactions involve the transfer of electrons between chemical species. The chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. 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.
As an example, during the combustion of wood, oxygen from the air is reduced, gaining electrons from carbon which is oxidized.[3] Although oxidation reactions are commonly associated with the formation of oxides from oxygen molecules, oxygen is not necessarily included in such reactions, as other chemical species can serve the same function.[3]
The reaction can occur relatively slowly, as with the formation of rust, or more quickly, in the case of fire. There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), and more complex processes such as the oxidation of glucose (C6H12O6) in the human body.
A good example is the reaction between hydrogen and fluorine in which hydrogen is being oxidized and fluorine is being reduced:
H
2 + F
2 → 2 HF
We can write this overall reaction as two half-reactions:
the oxidation reaction:
H
2 → 2 H+ + 2 e−
and the reduction reaction:
F
2 + 2 e− → 2 F−
Analyzing each half-reaction in isolation can often make the overall chemical process clearer. Because there is no net change in charge during a redox reaction, the number of electrons in excess in the oxidation reaction must equal the number consumed by the reduction reaction (as shown above).
Elements, even in molecular form, always have an oxidation state of zero. In the first half-reaction, hydrogen is oxidized from an oxidation state of zero to an oxidation state of +1. In the second half-reaction, fluorine is reduced from an oxidation state of zero to an oxidation state of −1.
When adding the reactions together the electrons are canceled:
H
2 → 2 H+ + 2 e−
F
2 + 2 e− → 2 F−
H2 + F2 → 2 H+ + 2 F−
And the ions combine to form hydrogen fluoride:
2 H+ + 2 F− → 2 HF
The overall reaction is:
H
2 + F
2 → 2 HF
Metal displacement
A redox reaction is the force behind an electrochemical cell like the Galvanic cell pictured. The battery is made out of a zinc electrode in a ZnSO4 solution connected with a wire and a porous disk to a copper electrode in a CuSO4 solution.
In this type of reaction, a metal atom in a compound (or in a solution) is replaced by an atom of another metal. For example, copper is deposited when zinc metal is placed in a copper(II) sulfate solution:
Zn(s)+ CuSO4(aq) → ZnSO4(aq) + Cu(s)
In the above reaction, zinc metal displaces the copper(II) ion from copper sulfate solution and thus liberates free copper metal.
The ionic equation for this reaction is:
Zn + Cu2+ → Zn2+ + Cu
As two half-reactions, it is seen that the zinc is oxidized:
Zn → Zn2+ + 2 e−
And the copper is reduced:
Cu2+ + 2 e− → Cu