Combustion of Fuels
The combustion or the burning of fuels, is perhaps the most common and obvious example of oxidation and reduction. Combustion is also that process which converts the potential energy of fuels into kinetic energy (heat and light). Most fuels (gasoline, diesel oil, propane, etc.) are compounds comprised primarily of carbon and hydrogen. These hydrocarbons represent an excellent source of potential energy which is released as heat during the combustion process. A common example is the oxidation of propane, the fuel used for gas ranges:
C3H8 + 5 O2 -----> 3 H2O + CO2 + Heat
As propane burns in air, its carbon atoms are oxidized when they combine with oxygen to form carbon dioxide. In turn, molecular oxygen is reduced by the hydrogen atoms, forming water. The heat produced can be used directly such as in the cooking of foods or to cause the expansion of the gaseous products produced to perform mechanical work such as in an internal combustion or steam engine.
Many other substances besides hydrocarbons can be used as fuels. For example, the alcohols, such as methanol (CH3OH) and ethanol (CH3CH2OH) are often used in racing cars. Ethanol mixed with gasoline, called gasohol , is currently being explored as a substitute for gasoline. Among the simplest fuels is molecular hydrogen (H2) which readily reacts with oxygen forming water as shown:
2 H2 + O2 ------> 2 H2O + Energy
The simplicity and "nonpolluting" aspect of this oxidation-reduction reaction, the amount of energy produced, and the relative abundance of both hydrogen and oxygen in our environment, makes hydrogen a very attractive alternative fuel source. Research efforts are currently focused on further developing the technology to broaden its use as a source of energy.
Saturday, August 29, 2009
Nitrogen Fixation(Application of redox reaction)
Nitrogen Fixation
Nitrogen is the most abundant element in our atmosphere. It is a vital element as many classes of compounds essential to living systems are nitrogen-containing compounds. Nitrogen is a primary nutrient for all green plants, but it must be modified before it can be readily utilized by most living systems. Nitrogen fixation is one process by which molecular nitrogen is reduced to form ammonia. This complex process is carried out by nitrogen-fixing bacteria present in the soil. Although nitrogen-fixation involves a number of oxidation-reduction reactions that occur sequentially, that reaction which describes its reduction can be written in a simplified way as:
N2 + 6 e- + 8H+ ---> 2 NH4+ (ammonium ion)
The ammonium ion (the conjugate acid of ammonia, NH3 ) that is produced by this reaction is the form of nitrogen that is used by living systems in the synthesis of many bio-organic compounds.
Another way by which ammonia may be formed is by the process called nitrification. In this process compounds called nitrates and nitrites, released by decaying organic matter are converted to ammonium ions by nitrifying bacteria present in the soil. The process carried out by these bacteria is also a complex series of oxidation-reduction reactions. The reduction reactions involving nitrate and nitrite ions can be simplified as:
NO3- + 2e- + 2H+ -----------> NO2- + H2O
(nitrate ion) (nitrite ion)
NO2- + 6e- + 2H+ ----------> NH4+ + 2 H2O
Another way in which molecular nitrogen is modified is via the discharge of lightning. The tremendous energy released by the electrical discharges in our atmosphere breaks the rather strong bonds between nitrogen atoms, causing them to react with oxygen. Note in this process, nitrogen is oxidized and oxygen is reduced.
lightning
N2 + O2 --------------> 2 NO (nitric oxide)
The nitrous oxide formed combines with oxygen to form nitrogen dioxide.
2 NO + O2 ---------------> 2NO2
Nitrogen dioxide readily dissolves in water to product nitric and nitrous acids;
2 NO2 + H2O -------> HNO3 + HNO2
These acids readily release the hydrogen forming nitrate and nitrite ions which can be readily utilized by plants and micro-organisms.
HNO3 --------> H+ + NO3- (nitrate ions)
HNO2 --------> H+ + NO2- (nitrite ions)
Denitrifying bacteria, act on ammonia as well as nitrates produced by death and decay, recycling these compounds as free nitrogen (N2). The nitrogen that is fixed by the processes described above is eventually returned to the atmosphere by this denitrification process, to complete what is commonly referred to as the "nitrogen cycle".
Nitrogen is the most abundant element in our atmosphere. It is a vital element as many classes of compounds essential to living systems are nitrogen-containing compounds. Nitrogen is a primary nutrient for all green plants, but it must be modified before it can be readily utilized by most living systems. Nitrogen fixation is one process by which molecular nitrogen is reduced to form ammonia. This complex process is carried out by nitrogen-fixing bacteria present in the soil. Although nitrogen-fixation involves a number of oxidation-reduction reactions that occur sequentially, that reaction which describes its reduction can be written in a simplified way as:
N2 + 6 e- + 8H+ ---> 2 NH4+ (ammonium ion)
The ammonium ion (the conjugate acid of ammonia, NH3 ) that is produced by this reaction is the form of nitrogen that is used by living systems in the synthesis of many bio-organic compounds.
Another way by which ammonia may be formed is by the process called nitrification. In this process compounds called nitrates and nitrites, released by decaying organic matter are converted to ammonium ions by nitrifying bacteria present in the soil. The process carried out by these bacteria is also a complex series of oxidation-reduction reactions. The reduction reactions involving nitrate and nitrite ions can be simplified as:
NO3- + 2e- + 2H+ -----------> NO2- + H2O
(nitrate ion) (nitrite ion)
NO2- + 6e- + 2H+ ----------> NH4+ + 2 H2O
Another way in which molecular nitrogen is modified is via the discharge of lightning. The tremendous energy released by the electrical discharges in our atmosphere breaks the rather strong bonds between nitrogen atoms, causing them to react with oxygen. Note in this process, nitrogen is oxidized and oxygen is reduced.
lightning
N2 + O2 --------------> 2 NO (nitric oxide)
The nitrous oxide formed combines with oxygen to form nitrogen dioxide.
2 NO + O2 ---------------> 2NO2
Nitrogen dioxide readily dissolves in water to product nitric and nitrous acids;
2 NO2 + H2O -------> HNO3 + HNO2
These acids readily release the hydrogen forming nitrate and nitrite ions which can be readily utilized by plants and micro-organisms.
HNO3 --------> H+ + NO3- (nitrate ions)
HNO2 --------> H+ + NO2- (nitrite ions)
Denitrifying bacteria, act on ammonia as well as nitrates produced by death and decay, recycling these compounds as free nitrogen (N2). The nitrogen that is fixed by the processes described above is eventually returned to the atmosphere by this denitrification process, to complete what is commonly referred to as the "nitrogen cycle".
Metabolism (Application of redox reaction)
Metabolism
Metabolism is a general term used to refer to all of the chemical reactions which occur in a living system. Metabolism can be divided into two parts; anabolism, or reactions involving the synthesis of compounds; and catabolism, or reactions involving the breakdown of compounds. In terms of oxidation-reduction principles, anabolic reactions are primarily characterized by reduction reactions, such as the dark reaction in photosynthesis where carbon dioxide is reduced to form glucose. Catabolic reactions are primarily oxidation reactions. Although catabolism involves many separate reactions, an example of such as process can be described by the oxidation of glucose as shown below. Note that this equation is the reverse of the photosynthetic equation.
C6H12O6 + 6 O2 ----------> 6 CO2 + 6 H2O + Energy
Note also, that in this reaction, the carbon atoms in glucose are oxidized, undergoing an increase in oxidation state (each carbon loses 2 electrons) as they are converted to carbon dioxide. At the same time, each oxygen atom is reduced by gaining 2 electrons when it is converted to water. Part of the energy is released as heat and the remainder is stored in the chemical bonds of "energetic" compounds such as adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NADH).
Catabolic reactions can be divided into many different groups of reactions called, catabolic pathways. In these pathways (referred to as Glycolysis, the Citric Acid Cycle, and Electron Transport) the carbon atoms are slowly oxidized by a series of reactions which gradually modify the carbon skeleton of the compound as well as the oxidation state of carbon. Coupled to these reactions are other reversible oxidation-reduction reactions designed to capture the energy released and temporarily store it within the chemical bonds of compounds called adenosine triphosphate (ATP) and nicotamide dinucleotide (NADH) . These compounds are then utilized to provide energy for driving the cellular machinery.
Metabolism is a general term used to refer to all of the chemical reactions which occur in a living system. Metabolism can be divided into two parts; anabolism, or reactions involving the synthesis of compounds; and catabolism, or reactions involving the breakdown of compounds. In terms of oxidation-reduction principles, anabolic reactions are primarily characterized by reduction reactions, such as the dark reaction in photosynthesis where carbon dioxide is reduced to form glucose. Catabolic reactions are primarily oxidation reactions. Although catabolism involves many separate reactions, an example of such as process can be described by the oxidation of glucose as shown below. Note that this equation is the reverse of the photosynthetic equation.
C6H12O6 + 6 O2 ----------> 6 CO2 + 6 H2O + Energy
Note also, that in this reaction, the carbon atoms in glucose are oxidized, undergoing an increase in oxidation state (each carbon loses 2 electrons) as they are converted to carbon dioxide. At the same time, each oxygen atom is reduced by gaining 2 electrons when it is converted to water. Part of the energy is released as heat and the remainder is stored in the chemical bonds of "energetic" compounds such as adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NADH).
Catabolic reactions can be divided into many different groups of reactions called, catabolic pathways. In these pathways (referred to as Glycolysis, the Citric Acid Cycle, and Electron Transport) the carbon atoms are slowly oxidized by a series of reactions which gradually modify the carbon skeleton of the compound as well as the oxidation state of carbon. Coupled to these reactions are other reversible oxidation-reduction reactions designed to capture the energy released and temporarily store it within the chemical bonds of compounds called adenosine triphosphate (ATP) and nicotamide dinucleotide (NADH) . These compounds are then utilized to provide energy for driving the cellular machinery.
Photosynthesis (Application of redox reaction)
Photosynthesis
An example of naturally-occuring biological oxidation-reduction reactions is the process of photosynthesis. It is a very complex process carried out by green plants, blue-green algae, and certain bacteria. These organisms are able to harness the energy contained in sunlight, and via a series of oxidation-reduction reactions, produce oxygen and sugar, as well as other compounds which may be utilized for energy as well as the synthesis of other compounds. The overall equation for the photosynthetic process may be expressed as:
6 CO2 + 6H2O --------> C6H12O6 + 6 O2
(glucose)
The equation is the net result of two processes. One process involves the splitting of water. This process is really an oxidative process that requires light, and is often referred to as the "light reaction". This reaction may be written as:
12 H2O -----------------------> 6 O2 + 24 H+ + 24e-
light or radiant energy
The oxidation of water is accompanied by a reduction reaction resulting in the formation of a compound, called nicotinamide adenine dinucleotide phosphate (NADPH). This reaction is illustrated below:
NADP+ + H20 -------> NADPH + H+ + O
(oxidized form) (reduced form) (oxygen)
This reaction is linked or coupled to yet another reaction resulting in the formation of a highly energetic compound, called adenosine triphosphate, (ATP). As this reaction involves the addition of a phosphate group (labeled, as Pi) to a compound called, adenosine diphosphate (ADP) during the light reaction, it is called photophosphorylation.
ADP + Pi ------------> ATP
Think of the light reaction, as a process by which organisms "capture and store" radiant energy as they produce oxygen gas. This energy is stored in the form of chemical bonds of compounds such as NADPH and ATP.
The energy contained in both NADPH and ATP is then used to reduce carbon dioxide to glucose, a type of sugar (C6H12O6). This reaction, shown below, does not require light, and it is often referred to as the "dark reaction".
6 CO2 + 24 H+ + 24 e- ------> C6H12O6 + 6 H2O
The chemical bonds present in glucose also contain a considerable amount of potential energy. This stored energy is released whenever glucose is catabolized (broken down) to drive cellular processes. The carbon skeleton in glucose also serves as a source of carbon for the synthesis of other important biochemical compounds such as, lipids, amino acids, and nucleic acids.
In simplest terms, the process of photosynthessis can be viewed as one-half of the carbon cycle. In this half, energy from the sun is captured and transformed into nutrients which can be utilized by higher organisms in the food chain. The release of this energy during the metabolic re-conversion of glucose to water and carbon dioxide represents the second half of the carbon cycle and it may be referred to as catabolism or "oxidative processes".
An example of naturally-occuring biological oxidation-reduction reactions is the process of photosynthesis. It is a very complex process carried out by green plants, blue-green algae, and certain bacteria. These organisms are able to harness the energy contained in sunlight, and via a series of oxidation-reduction reactions, produce oxygen and sugar, as well as other compounds which may be utilized for energy as well as the synthesis of other compounds. The overall equation for the photosynthetic process may be expressed as:
6 CO2 + 6H2O --------> C6H12O6 + 6 O2
(glucose)
The equation is the net result of two processes. One process involves the splitting of water. This process is really an oxidative process that requires light, and is often referred to as the "light reaction". This reaction may be written as:
12 H2O -----------------------> 6 O2 + 24 H+ + 24e-
light or radiant energy
The oxidation of water is accompanied by a reduction reaction resulting in the formation of a compound, called nicotinamide adenine dinucleotide phosphate (NADPH). This reaction is illustrated below:
NADP+ + H20 -------> NADPH + H+ + O
(oxidized form) (reduced form) (oxygen)
This reaction is linked or coupled to yet another reaction resulting in the formation of a highly energetic compound, called adenosine triphosphate, (ATP). As this reaction involves the addition of a phosphate group (labeled, as Pi) to a compound called, adenosine diphosphate (ADP) during the light reaction, it is called photophosphorylation.
ADP + Pi ------------> ATP
Think of the light reaction, as a process by which organisms "capture and store" radiant energy as they produce oxygen gas. This energy is stored in the form of chemical bonds of compounds such as NADPH and ATP.
The energy contained in both NADPH and ATP is then used to reduce carbon dioxide to glucose, a type of sugar (C6H12O6). This reaction, shown below, does not require light, and it is often referred to as the "dark reaction".
6 CO2 + 24 H+ + 24 e- ------> C6H12O6 + 6 H2O
The chemical bonds present in glucose also contain a considerable amount of potential energy. This stored energy is released whenever glucose is catabolized (broken down) to drive cellular processes. The carbon skeleton in glucose also serves as a source of carbon for the synthesis of other important biochemical compounds such as, lipids, amino acids, and nucleic acids.
In simplest terms, the process of photosynthessis can be viewed as one-half of the carbon cycle. In this half, energy from the sun is captured and transformed into nutrients which can be utilized by higher organisms in the food chain. The release of this energy during the metabolic re-conversion of glucose to water and carbon dioxide represents the second half of the carbon cycle and it may be referred to as catabolism or "oxidative processes".
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