Chemical reaction is process in which substances, known as reactant, undergo transformation to form new substances, known as product. The changes that occur are brought about through the breaking and forming of chemical bonds, which alter the chemical composition and properties of the involved substances.
The substances which take part in chemical reaction are call reactant and the substances which are formed as a result of chemical reaction are called product.
Type Of Chemical Reaction
01. Combination Reaction
02. Decomposition Reaction
03. Single Displacement Reaction
04. Double Displacement Reaction
05. Neutralization Reaction
06. Redox Reaction
07. Precipitation Reaction
08. Acid-Base Reaction
09. Complexation Reaction
10. Photochemical Reaction
11. Thermal Decomposition (pyrolysis) Reaction
Identification Of Chemical Reaction
- Evolution of gas
- Change in colour
- Change in state
- Change in temperature
- formation of precipitation
What Is Chemical Equation ?
Symbolic representation of chemical reaction in terms of symbols and formulas of reactant and the product which give idea about chemical change.
Carbon react with oxygen gas to produce carbon dioxide.
C + O₂ → CO₂
01. Combination Reaction
A combination or synthesis reaction is a process where two or more elements react together to give one, more complex compound. This reaction is generalized as follows :
A + B → AB
Chemical combination reactions form the bases of chemistry and occur naturally, while many others do in industrial applications.
Example
- Water forms when hydrogen, H₂ and oxygen, O₂ combine.
2H₂(g) + O₂(g) → 2H₂O(l)
- Nitrogen (N₂) reacts with hydrogen H₂ to form ammonia NH₃.
N₂(g) + 3H₂(g) → 2NH₃(g)
- Sodium (Na) reacts with chlorine gas Cl₂ to form sodium chloride NaCl.
2Na(s) + Cl₂(g) → 2NaCl(s)
- Carbon (C) combusts with oxygen to form carbon dioxide CO₂.
C + O₂(g) → CO₂(g)
- Heating calcium carbonate CaCO₃ gives calcium oxide CaO and releases carbon dioxide.
CaCO₃(s) → CaO + CO₂(g)
- Carbon with hydrogen forms methane, which is the most important natural gas.
C + 2H₂(g) → CH₄(g)
02. Decomposition Reaction
A decomposition reaction is a type of chemical reaction in which a single compound breaks into two or more simpler substances. The general form of a decomposition reaction is :
AB → A + B
In this reaction, compound AB decomposes to give two or more different substances, A and B.
- Hydrogen peroxide decomposition is the decomposition of hydrogen peroxide H2O2 to give water H2O(l) and oxygen O2.
2H2O2(l)⇨2H2O(l) + O2(g)
2NH₄NO₃(s) → 2N₂(g) + 4H₂O(l) + O₂(g
- Sodium bicarbonate (NaHCO₃) decomposes to sodium carbonate (Na₂C0₃), water (H₂O), and carbon dioxide (CO₂).
2NaHCO₃(s) → Na₂CO₃(s) + H₂O(l) + CO₂(g)
- Hydrogen chloride gas HCl decomposes thermally to give hydrogen gas H₂ and chlorine gas Cl2.
2HCl(g) → H₂(g) + Cl₂(g)
03. Single Displacement Reaction
Single displacement reaction is another name of the single replacement reaction, one of the classes of chemical reactions. Here, one element or ion replaces another in a compound. This displacement occurs if the reacting element is more reactive or more active in the activity series than the element it displaces in the compound.
A general form of a single replacement reaction is
A + BC → AC + B
In this reaction, one element displaces another from compound BC and forms a new compound AC and the released of that other element.
Example
- Zinc (Zn) displaces hydrogen in hydrochloric acid (HCl) to form zinc chloride
(ZnCl2 )and hydrogen gas (H2 ).
Zn + 2HCl → ZnCl2 + H2
- Magnesium (Mg) combines with hydrochloric acid (HCl) to give magnesium
chloride (MgCl₂) and hydrogen gas (H₂).
Mg + 2HCl → MgCl₂ + H₂
Iron (Fe) reacts with copper sulfate (CuSO₄) to produce iron sulfate (FeSO₄) and copper (Cu).
Fe + CuSO₄ → FeSO₄ + Cu
Here, in this reaction, iron displaces copper from copper sulfate.
- Aluminum (Al) reacts with hydrochloric acid (HCl) to give aluminum chloride
(AlCl₃) and hydrogen gas (H₂).
2Al + 6HCl → 2AlCl₃ + 3H₂
- Sodium (Na) reacts with water (H₂O) to give sodium hydroxide (NaOH) and
hydrogen gas (H₂).
2Na + 2H₂O → 2NaOH + H₂
In this reaction, sodium displaces hydrogen from water.
- Potassium, K burns in oxygen, O₂ to produce potassium oxide, K₂O.
4K + O2 → 2K₂O
04. Double Displacement Reaction
One of the types of chemical reactions is a double displacement reaction, also known as a double displacement reaction. This reaction occurs when the positive and negative ions of two compounds are interchanged with each other to produce two new compounds.
The general form of a double displacement reaction is as follows: In this reaction, compound AB reacts with compound CD to give compound AD and compound CB.
Formation of Precipitate (Insoluble Salt): The most common double displacement reaction is the formation of a precipitate.
Example
- Upon the mixture of two soluble salts, one of the products of which is insoluble precipitates out of the solution. For example, if silver nitrate is reacted with sodium chloride, the silver chloride is an insoluble salt formed that precipitates out from the solution, whereas sodium nitrate remains in solution.
AgNO₃ + NaCl → AgCl + NaNO₃
- Neutralization reaction: Double displacement reactions can also take place between an acid and a base to give salt and water. For instance, when hydrochloric acid reacts with sodium hydroxide, the products are sodium chloride and water.
HCl + NaOH → NaCl + H₂O
- In some double displacement reactions, one of the products is a gas. Form example, when hydrochloric acid reacts with sodium sulfide, hydrogen sulfide gas forms along with sodium chloride as a soluble product.
2HCl + Na₂S → H₂S + 2NaCl
- Formation of a Weak Acid When acetic acid, CH₃COOH reacts with sodium hydroxide, sodium acetate is formed along with water. As the other one is strong base, so the resulting acid will be acetic acid which is itself a weak acid.
CH₃COOH + NaOH → CH₃COONa + H₂O
- Formation of a Coordination Complex: Sometimes, double displacement reactions lead to the formation of complex ions or coordination compounds. For example, when silver nitrate (AgNO₃) reacts with ammonia (NH₃), a complex ion diamminesilver(I) ion ([Ag(NH₃)₂]⁺) is formed.
AgNO₃ + 2NH₃ → [Ag(NH₃)₂]⁺ + NO₃⁻
05. Neutralization Reaction
Neutralization reaction is one of the chemical reactions where an acid reacts with a base to give water and a salt. The characteristic of this chemical reaction involves hydrogen ions, H⁺, from the acid and hydroxide ions, OH⁻, from the base, as they combine to give water, H₂O and yield a salt.
General equation for a neutralization reaction
Acid + Base → Water + Salt
Here’s an example of a neutralization reaction
Hydrochloric Acid + Sodium Hydroxide → Water + Sodium Chloride.
The balanced chemical equation for this reaction is
HCl + NaOH → H₂O + NaCl
Hydrochloric acid (HCl) is an acid and Sodium hydroxide (NaOH) is a base. Water (H₂O) is formed and Sodium chloride, commonly known as table salt, is also a product.
This means that in a neutralization reaction, the acid cancels out the base in their properties as acids and bases; it results in a near neutral solution, pH 7. The salt thus formed is usually soluble in water and dissociates into its individual ions.
06. Redox Reaction
Redox reaction is a short form of “reduction-oxidation” reaction, which is the type of chemical reaction in which there is a transfer of electrons from one substance to another. In a redox reaction, oxidation is said to occur when a substance loses its electrons, and reduction occurs when a substance gains electrons.
Therefore, this change in electron transfer is the primary characteristic of the redox reaction. The general form of redox reaction is as follows :
Oxidized Substance → Reduction (Gain of Electrons)
Reduced Substance → Oxidation (Loss of Electrons)
Example
- Combustion of Hydrogen Gas (H₂) with Oxygen Gas (O₂)
2H₂ + O₂ → 2H₂O
Here, in the reaction Hydrogen (H₂) is oxidized.
It loses its electrons to form water (H₂O). Thus, this is a reduction half-reaction. Oxygen (O₂) is reduced. It gains its electron and forms water (H₂O). Thus, this is an oxidation half-reaction. The whole reaction encompasses the oxidation as well as the reduction :
2H₂ + O₂ → 2H₂O
The hydrogen atoms are oxidized; they lose their electrons and the oxygen atoms get reduced by gaining the electrons to combine in making water.
This is a combustion reaction; a substance reacts with another one in this case hydrogen, which gives out heat with the product as water.
- Formation of Rust (Corrosion of Iron)
4Fe + 3O₂ → 2Fe₂O₃In this reaction, iron (Fe) is oxidized to iron(III) oxide, which is commonly called rust, while oxygen (O₂) gets reduced.
- Sodium Hypochlorite Bleaching
NaOCl + H2O + 2e⁻ → NaOH + Cl⁻ + O2
In this reaction, sodium hypochlorite is reduced to form sodium hydroxide and oxygen gas is released leaving the latter as byproduct which causes bleaching action.
- Plant Photosynthesis
6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
- Photosynthesis : Carbon dioxide (CO₂) is reduced to glucose (C₆H₁₂O₆) and
water (H₂O) is oxidized to oxygen gas (O₂) with the release of glucose, using light energy.
- Electrochemical Cell Reaction (e.g., Galvanic Cell)
In electrochemical cells such as a galvanic cell, redox reactions take place between the two half-cells, namely, oxidation half-reaction and reduction half-reactions. This reaction generates electricity. For instance, in the zinc-copper galvanic cell, the reactions that will be involved include the following :
Oxidation (Zinc) : Zn → Zn²⁺ + 2e⁻
Reduction (Copper) : Cu²⁺ + 2e⁻ → Cu
These are examples of different types of redox reactions, which is a fundamental concept in chemistry and the basis of most of the important natural and technological processes for energy production, corrosion, and biological activity.
Read More : Carbon Disulfide
07. Precipitation Reaction
A precipitation reaction is a chemical reaction in which two soluble compounds in solution combine to form an insoluble solid, known as a precipitate. Often it results from the combination of two ions in solution to form a compound of very low solubility.
General Form of Precipitation Reaction:
Aqueous Compound 1 + Aqueous Compound 2 → Precipitate + Aqueous Products.
Major characteristic of the reaction is that it generates an insoluble solid. The solid precipitates out from the solution and settles on the bottom.
Example
- Precipitation of Silver Chloride (AgCl)
AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq)
In the reaction, Silver nitrate, (AgNO₃) is aqueous and Another aqueous compound that is dissolved in water is sodium chloride (NaCl).
When the two solutions are combined, a white solid, silver chloride (AgCl), forms as a precipitate and sodium nitrate (NaNO₃) remains in the solution.
The appearance of a solid precipitate, such as AgCl, means that a chemical reaction has occurred. Silver chloride is highly insoluble in water; thus, it falls out of the solution and can be separated from the rest of the liquid.
Precipitation reactions are quite frequently used in analytical chemistry to determine the presence of some ions in a given solution. The addition of a reagent that would react with a specific ion and result in the formation of a precipitate establishes the presence and concentration of the specific ion.
- Precipitation reaction is the reaction between barium chloride (BaCl₂) and sodium sulfate (Na₂SO₄) forming a barium sulfate (BaSO₄) precipitate :
BaCl₂ (aq) + Na₂SO₄ (aq) → BaSO₄ (s) + 2NaCl (aq)
In this reaction, the product is the sulfate of barium, an almost entirely insoluble compound. Thus when it forms as a precipitate, it is white, suspended in the solution. It serves as a test for sulfates in qualitative analysis.
08. Acid-Base Reaction
An acid-base reaction is also a neutralization reaction. This is the reaction in which an acid combines with a base to give the salt and water. It is the reaction in which the acidic properties of acid and the basic properties of base are canceled out with each other to give a salt, which is usually a compound of ionic form.
An acid-base reaction is also a neutralization reaction. This is the reaction in which an acid combines with a base to give the salt and water. It is the reaction in which the acidic properties of acid and the basic properties of base are canceled out with each other to give a salt, which is usually a compound of ionic form.
General form of an acid-base reaction is :
Acid + Base → Salt + Water
Example
- Hydrochloric Acid (HCl) + Sodium Hydroxide (NaOH) → Sodium Chloride (NaCl) + Water (H₂O)
The balanced chemical equation for this reaction is
HCl + NaOH → NaCl + H₂O
Hydrochloric acid (HCl) is an acid and Sodium hydroxide (NaOH) is a base. Sodium chloride (NaCl) is a salt that is formed. Water (H₂O) is also produced.
The neutralization of acidity or basicity is key, as hydrogen ions from an acid combine with hydroxide ions in the base to form water (H₂O), and the remaining combination would be ions that, together with the hydrogen ions and hydroxide ions, form salts as well.
- Sulfuric acid and potassium hydroxide; its reaction is generate Potassium Hydroxide (KOH) and Sulphuric acid (H₂SO₄) which ends with Potassium sulphate and produce H2O.
H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
- Nitric acid and calcium hydroxide with reaction and generate calcium nitrate and produce H2O.
Nitric Acid (HNO₃) + Calcium Hydroxide (Ca(OH)₂) → Calcium Nitrate + Water
2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O
- Acetic acid and Ammonium hydroxide with reaction and generate ammonium acetate and produce Water.
CH₃COOH + NH₄OH → NH₄CH₃COO + H₂O
09. Complexation Reaction
The term for complexation reaction or otherwise termed coordination reaction and complex formation reaction refers to any chemical reaction wherein the central metal atom or ion forms coordinate bonds with any ligand, either ionic or molecular in character, to give a complex ion or a coordination complex.
In a complexation reaction, the central metal atom or ion serves as a Lewis acid and accepts an electron pair from the ligands which serve as a Lewis base. Metal ion + Ligands → Complex Ion.
Example
- Formation of Hexaaquacobalt(II) Ion :
Co²⁺(aq) + 6H₂O(l) → [Co(H₂O)₆]²⁺(aq)
Co²⁺(aq) is a central metal ion, cobalt(II) Co²+ and H₂O(l) molecules are ligands that form coordinate bonds with the cobalt ion.
The resulting complex ion is [Co(H₂O)₆]²⁺(aq), often written as Co(H₂O)₆²⁺.The ligands of this complexation reaction include H₂O. This coordinates with cobalt(II) and produces a stable complex.
- The square brackets represent that the species is a complex ion. Formation of Tetraamminecopper(II) Complex :
Cu²⁺(aq) + 4NH₃(aq) → [Cu(NH₃)₄]²⁺(aq)
In this reaction, the NH₃ ligands or ammonia ligands form a complex with Cu²⁺ ions and produce the tetraamminecopper(II) complex ion.
Formation of Hexachloroplatinate(IV) Complex
PtCl₄²⁻(aq) + 6NH₄⁺(aq) → (NH₄)₂Ptcl6
Platinum(IV) chloride ions, PtCl₄²⁻ combine with ammonium ions, NH₄⁺ to produce ammonium hexachloroplatinate(IV) [(NH₄)₂[PtCl₆]].
- Tetraaquacobalt(II) Complex
Co²⁺(aq) + 4OH⁻(aq) + 4H₂O(l) → [Co(H₂O)₄(OH)₂]²⁻(aq)
The hexaaquacobalt(II) hydroxide complex results from the reaction of the equated cobalt(II) ions (Co²⁺), hydroxide ions (OH⁻), and water molecules (H₂O).
- Hexafluorosilicate(IV) Complex
SiF₆²⁻(aq) + 6H₂O(l) → [SiF₆]⁴⁻(aq) + 6H⁺(aq)
The water soluble Silicofluoride ions can dissociate into hydronium ions (H⁺) and the hexafluorosilicate(IV) ions, [SiF₆]⁴⁻
- Tetrachloromanganate(II) Complex
Mn²⁺(aq) + 4Cl⁻(aq) → [MnCl₄]²⁻(aq)
Manganese(II) ions combine with chloride ions to produce the tetrachloromanganate(II) complex ion.
Complexation reactions occur extremely frequently in chemistry. Most are of the highest significance in many areas. The ability of a great majority of the transition metal ions to combine easily with an especially diverse array of ligands means that complexation is often essential for many practical goals, including
- Chemical and industrial processes are catalysts used in organic synthesis.
- In analytical techniques like titration, concentration of the metal ions present in the sample is estimated by complexation reactions.
- Metal ions play a very crucial role in enzyme catalysis and other biological
processes.
- Coordination compound study including complexation reactions is one of the very big fields in chemistry and nowadays has much application in material science and nanotechnology.
- Complexation reactions are used in the treatment of water for the removal of metal ions from wastewater.
10. Photochemical Reaction
Photochemical reaction is a type of chemical reaction that is induced or heavily influenced by the absorption of light. Such reactions normally lead to the excitation of molecules to a higher energy level. Photochemical processes may now involve breaking or forming bonds among others.
Example
- Photosynthesis is a very common example of photochemical reaction. Here, with the aid of sunlight, carbon dioxide and water are assimilated by plants and certain other organisms into glucose, that is, form of sugar and oxygen gas, respectively.
- Chlorine gas may be decomposed into chlorine radicals (Cl•) by the ultraviolet light during photochemical reactions. These chlorine radicals may engage in many chemical reactions and degrade some organic compounds present in the atmosphere.
- In photocatalysis, the light energy can absorb materials like TiO₂ through which chemical reactions are catalytically initiated. For example, when UV light is shown, TiO₂ catalyzes the decomposition of water: H₂O into the two gases H₂ and O₂.
- Silver ions can be reduced photochemically to the formation of silver metal, Ag. This process is utilized in traditional photography. It provides the silver grains when light reaches the photographic film or paper.
- Certain alkenes dimerize in the photochemical reaction upon UV light. In this process, two molecules of the alkene combine to form a larger molecule. For example, two molecules of ethene, C₂H₄, dimerize upon photodimerization to form butene, C₄H₈.
2C₂H₄ → C₄H₈
11. Thermal Decomposition(pyrolysis) Reaction
Pyrolysis is the term for thermal decomposition. Thermal decomposition breaks a substance using heat. The chemical reaction is obtained by decomposing the compound with heat, and it is usually carried out in the absence of air or oxygen.
Example
- Limestone is calcium carbonate
CaCO₃ → CaO + CO
When calcium carbonate, CaCO ₃, a constituent of limestone, etc., is heated strongly, it decomposes to yield calcium oxide, lime, CaO, and carbon dioxide gas, CO₂.
- Decomposition of Hydrogen Peroxide
Reaction: 2H ₂ O ₂ → 2H ₂ O + O ₂
Description: Hydrogen peroxide, H ₂ O ₂ decomposes when heated to provide water, H ₂ O and oxygen gas, O ₂. This reaction is still widely utilized in the lab since several years for providing oxygen gas in the class of chemistry.
- Ammonium Nitrate Decomposition
NH₄NO₃ → N₂O + 2H₂O
Description: Ammonium nitrate is also another common fertilizer and explosive, and like many such fertilizers, decomposes thermally at fairly low temperatures into nitrogen dioxide and water vapor.
- Decomposition of Sodium Bicarbonate (Baking Soda)
2NaHCO₃ ⇌ Na₂CO₃ + H₂O + CO₂
Sodium bicarbonate, or baking soda (NaHCO₃), decomposes to sodium carbonate (Na₂CO₃), water (H₂O), and carbon dioxide gas (CO₂) when heated. The reaction is used in baking in the production of carbon dioxide gas that gives dough its rise.
- Pyrolysis of Organic Matter, which is Wood or Biomass.
It is a complex reaction where organic compounds decompose to various gases, liquids, and char.
In pyrolysis, the organic material is wood or biomass where the organic material is broken down to form simpler compounds, including hydrocarbons, gases, such as methane, ethylene, and solid char in a heating process without oxygen. This is used in the production of biochar and biofuels.
These are examples where application of heat onto various compounds or materials has caused their thermal decomposition. In fact, a really basic idea in chemistry that hence it gets direct applications in metallurgy, agriculture and materials science.
