We are very happy that you came to our website for the study. Chemistry; if somebody hears this particular subject’s name, it takes a second to imagine the first thing is the chemical reaction. On the other hand, studying various types of chemical reactions is fun. In this article, we will discuss the types of chemical reactions. But we have to know what is a chemical reaction in the first place.
Sometimes the substances in nature change in the chemical state due to pressure, heat as well as the contract of other substances, this change is known as the chemical reaction. For example, when a piece of iron (Fe) is deep into a concentrated sulfuric acid solution, the iron resolves in the acid and changes into iron(II) sulfate (FeSO4) and hydrogen (H2) gas. The chemical reaction is-
Fe + H2SO4 = FeSO4 + H2
Types of chemical reactions
Now, as we learn about chemical reactions, we can discuss the types of chemical reactions. The chemical changes can be classified in different ways. The classification could be as follow-
Based on the direction of the reaction
According to the direction, chemical reactions are of two types-
- Irreversible chemical reaction, and
- Reversible chemical reaction.
1. Irreversible reaction
The reaction in which only the reactants react and convert to product but the products do not further react with each other. To understand this type of reaction we should concentrate on an example; when calcium carbonate (CaCO3) is heated in an open vessel it is an Irreversible reaction. Because one of the products carbon-di-oxide (CO2) is a gas and leaves the reaction vessel immediately. Therefore, the products can not react with each other.
CaCO3(s) → CaO(s) + CO2(g)↑
2. Reversible reaction
When in a chemical reaction the reactants react to the product simultaneously, the products also react with each other and convert into reactants, then the chemical reaction is said to be a reversible reaction. To be clear we should look at an example. When ethanol (C2H5OH) and acetic acid (CH3COOH) react to form ethylacetate meanwhile the ethyl acetate (CH3COOC2H5) dissociates into the starting reactant materials. That’s why this reaction is a reversible reaction or a two-way reaction.
CH3CH2OH + HOOCCH3 ↔ CH3CH2OOCCH3 + H2O
Based on the changes in heat
Based on changes in heat during the reaction, chemical reactions are of two types. They are-
- An exothermic reaction, and
- Endothermic reaction.
1. Exothermic Reaction
The reaction or chemical changes when takes place, it releases energy usually in form of heat or light to the environment. That means heat evolves at the time of this certain chemical process. For example, when Hydrogen (H2) reacts with Nitrogen (N2) and produces 2mole ammonia (NH3) gas, it produces 92kj energy as heat at the same time.
3H2+ N2→ 2NH3; ΔH= -92kj
2. Endothermic reaction
These kinds of reactions are just the opposite of the above one. When this type of chemical action occurs the reaction system absorbs energy usually in the form of heat as well as light. For example, Nitrogen (N2) and Oxygen (O2) react with each other and produce 2 moles of Nitric oxide (NO) at the same time it takes up 180kj energy from the surroundings.
N2 + O2 → 2NO; ΔH= +180kj
Based on the changes in the Oxidation state (or electron transfer)
Depending on the electron transfer reactions are mainly two types. They are-
- Redox reaction, and
- Non-Redox reaction.
a. Redox Reaction
Redox word comes from two words; Reduction and oxidation. The first portion of the word Redox is ‘Red’ comes from reduction as well as the second portion ‘ox’ comes from the word Oxidation. That means the Redox reaction is basically the oxidation-reduction reaction. The chemical changes which are occurred by transferring electrons among the reactants, which means the oxidation state change. For example, when Na and Cl2 react with each other to produce the NaCl, Na releases one electron meanwhile the Cl atom accepts that electron released by the Na atom. In this particular reaction, electron transfer takes place.
2Na – 2e– → 2Na+ (electron released)
Cl2 + 2e– → 2Cl– (electron accepted)
2Na + Cl2 → 2NaCl (electron transfer)
There are a few reactions where oxidation-reduction occurred. Now, let’s discuss those reactions. The reactions are-
- Addition reaction,
- Decomposition reaction,
- Substitution (Displacement) reaction, and
- Combustion reaction.
1. Addition reaction
When at least two or more elements or compounds react to produce a new compound, this chemical change is known as the addition reaction. For example, FeCl2 and Cl2 react to produce FeCl3. This is an addition reaction and also a Redox reaction as well. Because electron transfer takes place in this certain chemical action.
FeCl2 + Cl2 → FeCl3
2. Decomposition reaction
The particular chemical changes in which a compound breaks down to its component elements or compound is called decomposition reaction. For example, when PCl5 breaks down and produces PCl3 and Cl2. The Oxidation state changes in this chemical action.
PCl5 → PCl3 + Cl2
3. Substitution (Displacement) reaction
The process in which an element or radical reacts with another compound and displaces or substitutes an atom or radical from the compound and takes its place. For example, Fe reacts with H2SO4 and displaces the H atoms to produce FeSO4 as well as H2. It is a Redox reaction.
Fe + H2SO4→ FeSO4 + H2
4. Combustion reaction
The chemical action in which an element or a compound reacts with Oxygen (burns) to produce respective oxide. For example, when CH4 burn in the cooker, it produced H2O as well as CO2. The electron transfers in this type of reaction as well.
CH4 + O2 → H2O + CO2
Combustion reaction means the reaction with Oxygen to produce Oxides and of course heat. The most interesting fact about this category of chemical changes is electron transfer occurred in this particular type of chemical reaction.
b. Non-Redox Rection
The reaction in which there is no exchange of electrons among the reactants is called a non-redox reaction. As there is no exchange of electrons, it does not involve any kind of change of oxidation state in this type of chemical change. Some of these types of reactions are- 1. Neutralization reaction, 2. Precipitation reaction, etc.
1. Neutralization reaction
The chemical change is in which the equivalent amount of acid and base react with each other to neutralize each other into corresponding salt and water. This type of chemical action is also known as the acid-base reaction. NaOH and HCl for example, react and neutralize each other and produce water along with NaCl (salt).
NaOH + HCl → NaCl + H2O
2. Precipitation reaction
The reaction in which two soluble compounds mix in a certain solvent and then if a new compound is formed which is insoluble or barely soluble in that solvent. Then the newly produced compound settled down at the bottom of the reaction vessel. This is called precipitation as well as this type of reaction is the precipitation reaction. For Example, if AgNO3 and NaCl are mixed then they react to produce NaNO3 and AgCl. The AgCl is insoluble in the water. So it precipitated from the reaction medium and settled at the bottom of the reaction vessel.
AgNO3 + NaCl → NaNO3 + AgCl ↓
3. Hydrolysis reaction
The chemical process in which, the water acts as a reactant and reacts with other compounds is a hydrolysis reaction. For example, when SiCl4 is mixed with water, it reacts with water and produces Si(OH)4.
SiCl4 + H2O → Si(OH)4 + HCl
4. Hydration reaction
When a crystal lattice is formed, one or more molecule of water has to combine with the ionic compound. This is the hydration reaction. The water which combines with the ionic compound is known as lattice water. For example, 5 moles of water is added with the CuSO4 compound to form a copper sulfate crystal lattice.
CuSO4 + 5H2O → CuSO4.5H2O
5. Isomerization reaction
When in a chemical reaction the atoms or radicals in a compound are rearranged and produce another compound of the same atomic mass and the chemical formula but a different molecular structure, this kind of chemical change is the isomerization reaction. Therefore, the main theme is, that in this reaction isomers are formed. For example, when ammonium cyanate solution is heated, then the atoms are rearranged and produce urea. The chemical formula of urea and ammonium cyanate are the same, but their molecular structures of them are different. So they are isomer of each other.
NH4CNO → NH2-CO-NH2
6. Polymerization reaction
The chemical processes in which a large number of molecules of the same compound are combined to produce a large molecular compound with a repeating group(s) and a large molecular mass under high temperature and pressure.
For example, under 1200atm pressure and 2000C temperature and the presence of O2 catalyst, a large number of tremendously small molecules of ethene combine to produce the molecular compound polyethylene which has a very large molecular mass.
n(CH2=CH2) → -(CH2-CH2-)n