Before we proceed with types of chemical reactions, we should firstly give an exact definition of a chemical reaction.
A chemical reaction can be defined as a process, leading to the complete transformation of one set of substances into another. When any chemical reaction takes place, only the positions of electrons in the breaking and creating of chemical bonds between atoms change, while the nuclei remains immutable.
The substances involved in a chemical reaction are known as reagents or reactants. Chemical reactions are traditionally characterized by a chemical change. They give one or several products with properties different from reactants.
A typical chemical reaction suggests a sequence of sub-steps, known as elementary reactions. The reaction mechanism matters too. It’s the actual information as for the precise course of action. Chemical reactions can be described by means of corresponding chemical equations, symbolically presenting the starting materials, intermediate products, end products as well as reaction conditions.
Chemical reactions take place at the so-called characteristic reaction rate, at a certain temperature as well as chemical concentration. As usual, reaction rates tend to grow with increasing temperatures. It’s because there’s more thermal energy released to reach the activation energy required to break bonds between atoms.
Reactions can proceed in the forward as well as reverse direction until they finish or gain equilibrium. Those reactions, which proceed in the forward direction in order to approach equilibrium are dubbed spontaneous. They don’t need input of free energy to proceed. Unlike the previous reactions, non-spontaneous ones can’t do without input of free energy. A typical example of a non-spontaneous reaction is charging a battery by simply applying an external electrical power source.
Different chemical reactions are employed in combinations in the process of chemical synthesis to get the required product. A consecutive series of chemical reactions form metabolic pathways in biochemistry. The given reactions are usually catalyzed by protein enzymes.
Enzymes raise the rates of biochemical reactions. As a result, decompositions and metabolic syntheses normally impossible under ordinary conditions, can take place at the concentrations and temperatures present in a cell.
The general concept of a chemical reaction has spread to reactions between particles, smaller than atoms. These are radioactive decays, nuclear reactions as well as reactions between elementary particles, described in quantum field theory.
There are many types of chemical reactions, varying from highly devastating nuclear reactions to allergic reactions. By the way, those reactions arising in Chemistry and Physics, are absolutely different from biological reactions. As the name suggests, biological reactions are associated with the body and they deal with the formation of bacteria, triggering negative symptoms in it. A typical example of a biological reaction is an allergic reaction.
Every chemical reaction boasts its own kinetics, suggesting energy changes. Some reactions undergo radical energy changes. They can be exothermic or endothermic. It’s a crucial nuance in the study of chemical reactions.
Since, chemistry is a must-have thing in any today’s industry, and chemical reactions in the making of a products are a common procedure now, a detailed analysis of every chemical reaction is expected to assist in proper manufacturing of the assigned stuff.
Some reactions are extremely inflammable. For instance, the combustion of methane or petrol is a very exothermic reaction, as a result of which, tons of heat are released.
Before we start discussing various types of chemical reactions, it makes sense to make a clear difference between chemical and nuclear reactions. Unfortunately, some younger learners are completely unaware of the fact that both these reactions are absolutely different things. Perhaps, this ignorance may be due to the evident lack of conceptual understanding of the structure of an atom.
An atom consists of a central nucleus with neutrons and protons packed in it. As for an electron, the third particle, it keeps circling around the nucleus. All the chemical reactions are associated with the loss, gain, transfer and sharing of electrons.
On the other hand, nuclear reactions are solely associated with the nucleus of the atom, and they’ve got nothing to do with electrons. Apart from that, nuclear reactions suggest decomposition of the nucleus. As a result, because of the loss of neutrons and protons, a new atom arises.
In general, a chemical reaction boasts a relatively low energy change, while a nuclear reaction normally proceeds with a significant change.
In fact, there’re lots of ways to classify chemical reactions. It’s a common occurrence that different authors make use of different approach to classifying chemical reactions. This can be explained by a variety of chemical transformations happening in the atoms as well as molecules when they react. Here, we’re going to use the most common approach to classifying reactions in chemistry. So, let’s illustrate the most common types of chemical reactions.
As the name suggests, the given reaction boasts several names. It’s a relatively simple type of reaction, compared to a decomposing reaction. In this case, two or even more different elements come together to form a new substance, that’s more complex compared to the reacting ones.
A typical example of this type of reaction is the formation of NaCl:
2Na + Cl2---------------------> 2NaCl
This type of reaction takes place when any substance is burnt in the presence of oxygen. Of course, you know that oxygen normally supports combustion. Oxygen is capable of burning anything by providing insignificant amounts of energy. Such reactions traditionally proceed with organic materials.
Sure, you’re already familiar with a typical combustion reaction. We’re talking about the burning of methane.
CH4 + 2O2 ---------------------> CO2 + 2H2O
It has nothing common with an addition reaction. In this case, a compound splits up into two or more simpler substances, which might be compounds and elements. Energy is required to power these reactions, making them fully endothermic.
A true example of a decomposition reaction is decomposition of calcium carbonate.
CaCO3 -------------------> CaO + CO2
In this particular case, one element simply displaces another element from a compound. As a result, in the compound one atom is replaced with another. By the way, the elements, replacing another atom need to be reactive enough. Otherwise, the reaction might not proceed.
For instance, let’s have a look at hydrogen is displaced from HCl.
2Na + 2HCl -------------> 2NaCl + H2
That’s the final type of reaction and probably the most complicated one. Here, an exchange of atoms between two different compounds occurs. This gives different products. A typical outcome of this type of reaction is an undissolved or precipitate substance. Such reactions are quite common with bases and acids.
For instance, let’s have a look at the formation of silver chloride.
NaCl + AgNO3----------------------> NaNO3 + AgCl
Chemical reactions, including reduction of ores to metals, fermentation and combustion were well known since antiquity. The first theories of transformation of materials were developed by Greek philosophers. For instance, they created the Four-Element Theory of Empedocles. According to that theory, any substance consists of the four key elements – water, fire, earth and air. In the Middle ages, chemical transformations were explored by alchemists. Their greatest dream was to turn lead into gold. For this purpose, they employed reactions of lead as well as lead-copper alloys with sulfur.
The production of chemical substances, which never normally take place in nature has been tried for a long time. As typical examples, we can point out to the synthesis of nitric acids and sulfuric attributed to the skilled and quick-witted alchemist Jabir ibn Hyyan. The process involved heating of nitrate and sulfate minerals, including alumand saltpeter as well as copper sulfate.
In the 17th century, Johann Rudolph Glauber managed to produce sodium sulfate and hydrochloric acid. That was a reaction of sodium chloride and sulfuric acid. With the overall development of the lead chamber process and Leblanc process in 1746, it became possible to organize large-scale production of sodium carbonate and sulfuric acid. That was a debut of chemical reactions in the industry. Then, further optimization of sulfphuric acid technology gave us the contact process by the end of the 19th century, while the Haber process for ammonia synthesis was developed for 1909-1910.
From the 16th century, such researchers as Isaac Newton, Robert Boyle, Jan Baptist van Helmont did their best to work out solid theories of the experimentally observed chemical transformations. In 1667, Johann Joachim Becher established the phlogiston theory. It actually postulated the existence of a fire-like element dubbed «phlogiston», that could be contained in combustible bodies and accordingly released in the process of combustion. However, in 1785 Antoine Lavoisier proved its false nature. Antoine managed to find an adequate explanation of the combustion. From his point of view, combustion was just a reaction of the air and oxygen.
In 1808, Joseph Louis Gay-Lussac found out that gases are used to reacting in a certain relationship with each other. Using this idea as well as the atomic theory of John Dalton, Joseph Proust worked out the law of definite proportions, later resulted in the concepts of chemical equations and stoichiometry.
As for organic chemistry, for a long time it was believed that compounds obtained from living organisms couldn’t be synthesized due to their complexity. In accordance with the concept of vitalism, organic matter was stuffed with a vital force and stood away from inorganic materials. This separation was completely debunked by the synthesis of urea from inorganic precursors in 1828 by Friedrich Wohler. As for other chemists, who made decent contributions to organic chemistry, we should point out to Christopher Kelk Ingold with his mechanisms of substitution reactions and Alexander William Williamson with his synthesis.
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