**5. Redox reactions in explosion reactions**

glucose to O<sup>2</sup>

to cause cancer [7].

is, electrons are lost or gained in each step.

6 Redox - Principles and Advanced Applications

**3. Redox reactions in corrosion reactions**

**4. Redox reactions in combustion reactions**

is thermodynamically downhill, and cells use this released energy to carry out

a wide variety of energy‐requiring activities. **Figure 1** illustrates how glucose is burned in a series of redox reactions and ends up in the formation of carbon dioxide and energy that is stored as adenosine triphosphate (ATP); in the diagram called Krebs Cycle which describes cell burning of glucose, enzymes are used in each step to lower the activation energy for each step and aid in breaking and formation of bonds; the overall reaction is a redox reaction, that

Other biological processes that involve the redox reaction is the production of free radicals, which can be produced by detaching electrons from certain type of molecules and reattaching to another type of molecule instantaneously; free radicals play an important role for the pro‐ grammed cell death (apoptosis), and any uncontrolled production of free radicals may lead

Corrosion is another type of redox reaction; it occurs when a metal comes in contact to a solution or at least moisture; the metal corrodes with evolving of electrons that move to cathodic part of the so‐called localized galvanic cell, and then, cathodic reaction starts with the production of hydrogen gas if the electrolyte is acidic or conversion of water to hydroxide if the electrolyte is neutral or basic. In this case, the intensity of flow of electrons from the anodic part (metal) to cathodic part (electrolyte) is defined as the corrosion current; there may be some microscopic galvanic cells with adjacent distance or some distance apart if the electric current in the galvanic cells is huge and is more than the electrolyte capacity to allow the current to pass, then the opera‐ tion is governed by the movement of electrolyte ions; on the other hand, if the electric current is less than the electrolyte capacity to allow the current to pass, then the operation is governed by activation energy. One of the famous corrosion examples is the iron rust, and in this case, iron is oxidized at the beginning to ferrous ions releasing two electrons, and the reaction will proceed as long as the metal is capable of releasing electrons and electrolytic solution to carry the ions; the corrosion current is increased by increasing the number of oxidized iron atoms, and if there is excess of oxygen in electrolyte, then ferrous ions are oxidized further to ferric ions that can give ferric oxide or ferric carbonate which is the main constituent of the iron rust. Besides iron, most of elements in the periodic table are capable to corrode, and corrosion now has become a global problem that should be controlled if it could not be stopped (according to the second law of thermodynamics); the biggest breakthrough that has been achieved in the corrosion research is the invention of the electrochemical series, a series in which ordering the periodic table ele‐ ments depends on the redox potential, and the most benefit of this is trying not to gather two ele‐ ments of far different reduction potential in one alloy because that is produced in fast corrosion.

To start a discussion on this, let us first ask this question, is the combustion reactions is a redox reaction? Answering this, as the oxidation state is changed from 0 in the molecular oxygen to −2 Potassium nitrate, when mixed with carbon and sulfur in correct ratios which are the constitu‐ ents of gunpowder, nitrate is reduced to form nitrogen, mono and dioxides, while carbon is oxidized to form carbon mono and dioxides, and sulfur is oxidized to form di and trioxides. The reaction will not start unless it is initiated; it has been found that such reactions can be initiated by electric shocks, spark, or electric current, and the reaction is maintained in a series of complicated steps; production of all these gases increase suddenly the pressure, the contents of the reaction come to explode to relieve the pressure, and besides increase in pressure, tem‐ perature is also increased tremendously; the main mechanism of explosive reaction is the chain reaction by which one product of the reaction, called free radical, is initiated and activates other molecules in the reaction mixture, and the reaction is proceeded till all free radicals are used up.

Although nuclear explosion is one of the massive explosions on earth, but is not itself a redox reaction, and is something more complicated, as in the case of uranium, the nuclei split and form two different elements and release energy more than any ordinary explosive.

Nowadays, redox reactions fuel the most advanced form of the space transportation and the space shuttle; powdered aluminum and ammonium perchlorate are used to undergo redox reactions that produce the gases hydrogen and oxygen and give the shuttle enormous amount of extra thrust; the redox reaction is represented as follows:

$$\text{3NH}\_4\text{ClO}\_{4(s)} + \text{3Al}\_{(s)} \rightarrow \text{Al}\_2\text{O}\_{3(s)} + \text{AlCl}\_{3(s)} + \text{3NO}\_{(g)} + \text{6H}\_2\text{O}\_{(g)} + \text{energy} \tag{1}$$

It produces temperatures of about 5700 F and 3.3 million pounds of thrust in each rocket; thus, the redox reactions furnish the energy to launch the space shuttle.

## **6. Conclusions**

Besides the above examples, so many examples can be drawn to prove the importance of applica‐ tions of redox reactions in general life; in electrochemical cells, electrons formed from the oxida‐ tion of one element and pass through a conductor to the reduction element; bleaching solutions that are used to brightening clothes are made of oxidizing agent (clorox), and this oxidizes any constituent that is capable of being oxidized and then make clothes clean and bright, and so on.

In this summarized introduction, we aimed to draw the reader's attention to the wide range of applications as well as the importance of redox reactions; luckily, chapters of this book can be categorized into two main parts: Part (1) batteries and computer applications and part (2) drugs and biological applications, and the diverse of chapters exhibit clearly the wide range of researches in the field of redox reactions.
