Combustion, redox reaction

Redox reactions constitute the third of the three major classes of chemical reactions treated here. The variety of these reactions is remarkable. Many common reactions, such as combustion, corrosion, photosynthesis, the metabolism of food, and the extraction of metals from their ores, appear to be completely different. However, when we consider these changes at the molecular level with a chemist s eye, we can see that they are all examples of a single type of process. 

The membrane-separated reductant and oxidant formed upon PET can be used for accomplishment of various catalytic redox reactions which provide conversion of the chemical energy of a (D. ..A ) pair into the chemical energy of a pair of more stable species such, e.g., as H2 and O2 molecules. This stored energy can be released when necessary in the form of high potential heat or electricity via combustion of H2 + 1/2 O2 mixture in a furnace or fuel cell. 

By far the most important redox reaction relative to chemical stability is the reaction between an oxidizable material and oxygen from air. The particle size and any droplets have a large effect on the combustion properties. Some substances react so rapidly in air that ignition occurs spontaneously. These so called pyrophoric compounds (white phosphorus, alkali metals, metal hydrides, some metal catalysts, and fully alkylated metals and nonmetals) must be stored in the absence of air. 

Oxidation-reduction reactions, commonly called redox reactions, are an extremely important category of reaction. Redox reactions include combustion, corrosion, respiration, photosynthesis, and the reactions occurring in batteries. 

Oxidation—reduction reactions, commonly called redox reactions, are an extremely important category of reaction. Redox reactions include combustion, corrosion, respiration, photosynthesis, and the reactions involved in electrochemical cells (batteries). The driving force involved in redox reactions is the exchange of electrons from a more active species to a less active one. You can predict the relative activities from a table of activities or a halfreaction table. Chapter 16 goes into depth about electrochemistry and redox reactions. 

Combustion reactions are redox reactions in which the chemical species rapidly combines with oxygen and usually emits heat and light. Reactions of this type are extremely important in our society as the sources of heat energy. Complete combustion of carbon yields carbon dioxide, and complete combustion of hydrogen yields water. The complete combustion of hydrocarbons, organic compounds containing only carbon and hydrogen, yields carbon dioxide and water ... 

Combustion reactions are redox reactions in which the chemical species rapidly combine with diatomic oxygen gas, emitting heat and light. The products of the complete combustion of a hydrocarbon are carbon dioxide and water. 

In your previous chemistry course, you classified reactions into four main types synthesis, decomposition, single displacement, and double displacement. You also learned to recognize combustion reactions and neutralization reactions. You have now learned to classify redox reactions. In addition, you have also learned about a special type of redox reaction known as a disproportionation reaction. 

In the next investigation, you will carry out several redox reactions, including reactions of acids with metals, and the combustion of hydrocarbons. 

Predict whether the combustion of a hydrocarbon is a redox reaction. What assumptions have you made about the products ... 

Are combustion reactions also redox reactions Does your answer depend on whether the combustion is complete or incomplete Explain. 

In this section, you learned the half-reaction method for balancing equations for redox reactions. You investigated the redox reactions of metals with acids, and the combustion of two hydrocarbons. After applying the half-reaction method in the following review problems, you will learn a different method in section 10.4. This method will make greater use of oxidation numbers. 

Fig. 126. Thermal layer model of combustion of solid composite propellant with ammonium nitrate, according to Chaiken [2] R—redox reaction flame zone (temperature 7f), u—gas velocity, S—thickness of the thermal layer, T —surface temperature of oxidizer particle, ro—radius of oxidizer particle.

Not all reactions are redox reactions. Only the ones in which electrons are transferred from one reactant to another are classified as redox reactions. Many single-displacement reactions, combination reactions, decomposition reactions, and combustion reactions are redox reactions. Double displacement reactions never involve the transfer of electrons and are not, therefore, redox reactions. Since acid-base reactions are just a special type of double displacement reaction, they cannot be redox reactions, either. 

The possibility that oxidation numbers may change among the reactants indicates an electron transfer and a redox reaction. Combustion reactants consist of an organic molecule and oxygen. 

Oxidation and reduction are two sides of the same coin, in that oxidation is about the loss of electrons and reduction is about the gain of electrons. Within any chemical reaction, if oxidation is occurring, reduction is also taking place. This simultaneous occurrence of oxidation and reduction is called redox, a combination of the words reduction and oxidation. The redox reactions of our everyday life include respiration, rusting, all combustion, and most metabolic reactions in living organisms. 

It should be noted that an explosion differs from ordinary combustion in two very significant ways. First, oxygen from the air is not a major reactant in the redox reactions of most explosives. The source of oxygen (or other reducible species) needed for reaction with the fuel—the oxidizer—may be part of the same molecule as the fuel or a separate intermixed material. Thus an explosive may be thought of as merely an intimate mixture of oxidizer and fuel. This degree of intimacy contributes to the second significant difference between an explosion and norma] combustion—the speed with which the reaction occurs. 

The available data concerning the effect of metal compounds on the pyrolysis and combustion of polymeric materials show that there is a great potential in the control of these materials, This field is still in its embryonic stage. Much is yet unclear. In many cases the analysis is rendered difficult because of the dual function of metal compounds (especially of the d- and f-types) in redox reactions. Their ability not only to inhibit but also to promote polymer decomposition manifests itself most clearly in concentration effects The specific effects of certain metal compounds on the ignition and combustion rate of polymers indicate that heterogeneous oxidation... 

As our quick trot from prehistoric chemistry to the French Revolution might indicate, paired reduction-oxidation reactions, or redox reactions, have played a continuing role in the history of humankind. In our one-sentence survey of prehistoric chemistry, we did not include an extremely important redox reaction—the making of fire—but we include it now because combustion, it turns out, is one of the most famous, and infamous, redox reactions. 

The primary combustion reaction is a straightforward redox reaction. A compound made primarily of hydrogen and carbon, a hydrocarbon, is usually the fuel. When hydrocarbons mix with oxygen, they can react to produce carbon dioxide (CO2) and water and heat. 

As we saw in our discussion of redox reactions, combustion reactions can travel through the gas phase quite rapidly. Solvent fumes, likewise, can be quite flammable, which is why they should be used away from any sparks or open flame and in a well-ventilated space. The liquid solvent... 

The reaction of magnesium and oxygen involves a transfer of electrons from magnesium to oxygen. Therefore, this reaction is an oxidation-reduction reaction. Using the classifications given in Chapter 10, this redox reaction also is classified as a combustion reaction. 

Oxidation-reduction reactions are among the most important in chemistry, biochemistry, and industry. Combustion of coal, natural gas, and gasoline for heat and power are redox reactions, as are the recovery of metals such as iron and aluminum from their oxide ores and the production of chemicals such as sulfuric acid from sulfur, air, and water. The human body metabolizes sugars through redox reactions to obtain energy the reaction products are liquid water and gaseous carbon dioxide. 

Define combustion. Why are all combustion reactions also redox reactions ... 

However redox reactions of alkanes, in particular with oxygen and the halogens, are possible as the carbon atoms are in a strongly reduced condition in the case of methane, the lowest possible oxidation state for carbon (-4) is reached. Reaction with oxygen leads to combustion without any smoke with halogens, substitution. In addition, alkanes have been shown to interact with, and bind to, certain transition metal complexes. 

Based on the above discussion, the function of the wet-oxidation catalysts should be confined to (i) activation of oxygen and (ii) direct electron transfer with the reactants (redox reaction) in the first step of the reaction. CeO seems to effectively contribute to both factors. CeOj behaves quite differently from other oxides of lanthanide and is always a constituent of automobile-exhaust purification catalysts. It stabilizes supports and keeps high surface area [64,65], prevents the sintering of precious metals and, thus, stabilizes their dispersed state [66,67], and acts as an oxygen reservoir [68,72]. When combined with precious metals, it works in various reactions other than the purification of vehicle exhausts e.g., detoxification of NjO, methanol decomposition, methanol synthesis, combustion of formaldehyde, etc [47,73-75]. Precious metals are remarkably activated and behave quite differently on CeO compared with their action on other supports. 

Does this type of reaction look familiar You learned in Chapter 6 that this is classified as a synthesis reaction. You also know that early chemists called it an oxidation reaction because oxygen is a reactant. The formation of zinc oxide falls into another, broader class of reactions characterized by the transfer of electrons from one atom or ion to another. This type of reaction is called an oxidation-reduction reaction, commonly known as a redox reaction. Many important chemical reactions are redox reactions. Formation of rust is one example combustion of fuels is another. In each redox reaction, one element loses electrons, and another element takes them. 

---