Types of Chemical Reactions - Explanation, Examples, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:42 PM IST

What is a Chemical Reaction?

A chemical reaction occurs when the bonds between reactant molecules are broken and new bonds are established between product molecules, resulting in the formation of a new substance. The reactants are the substances that react during a chemical reaction, whereas the products are the chemicals that are created during a chemical reaction. Chemical reactions may be found everywhere around us, from our bodies' food metabolism to how the light we receive from the sun is produced through chemical reactions. It is crucial to understand physical and chemical changes before starting with chemical reactions.

This Story also Contains

What is a Chemical Reaction?
Types of Chemical Reactions with Example
Difference Between Combination and Decomposition Reaction

The best example of physical and chemical change is a burning candle. Take a candle and put it on the table. We can see how the candle turns to wax as time goes on. The candle will go out if you cover it with a jar. The burning of the candle is a chemical change, whereas the conversion of the candle to wax is a physical change in the demonstration. A physical change primarily results in a change in the state of the substance, whereas a chemical change primarily results in the formation of a new substance in which energy is either released or absorbed. As a result, we can deduce that chemical changes are followed by physical modifications.

Types of Chemical Reactions with Example

Chemical reactions are classified into several categories based on a variety of characteristics.The list of various types of chemical reactions are:

Decomposition Reaction
Combination Reaction
Combustion Reaction
Neutralisation Reaction
Single displacement Reaction
Double Displacement Reaction
Precipitation Reaction
Redox Reaction

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Decomposition Reaction

Molecules or compounds decompose into two or more simpler chemically new entities in a decomposition reaction. Take, for example, water electrolysis. Water breaks down into hydrogen and oxygen during electrolysis, which have completely different properties than water.

Electrolysis of Water

Combination Reaction

Combination reaction definition: Two or more molecules are chemically joined to generate a new substance (compound) in a combination reaction. The reactions of combination and decomposition are completely contradictory.

Example of combination Reaction : When we burn magnesium ribbon (or magnesium), we get grey – black ash of magnesium oxide.

2 Mg + O₂ → 2 MgO

Types of Combination Reaction

1. An element combines with another element to generate a new compound in the first type of combination reaction.

Example: When nitrogen and hydrogen are run over finely split iron, they react to form ammonia, a pungent-smelling gas.

N₂ + 3 H₂ → 2 NH₃

2. An element combines with a compound in the second types of reaction.

When a chemical SO2 reacts with oxygen to form sulphur trioxide as an example.

2SO₂ + O₂ → 2SO₃

3. Two or more compounds mix to generate a new compound in the third type of combination.

Example: Slaked lime is a reaction in which lime reacts vigorously with water to produce a white powder of Calcium hydroxide.

CaO + H₂O → Ca(OH)₂

Combustion Reaction

It is a type of exothermic reaction that releases energy in the form of heat. It is a reaction that occurs when fuel reacts with an oxidant (usually air oxygen) to generate smoke, water, and heat. When we burn methane, for example, we get carbon dioxide and water.

CH₄ + 2 O₂ → CO₂ + 2 H₂O

Neutralization Reaction

Acid and base react with each other to produce salt and water in the neutralisation reaction. Hydrochloric acid, for example, interacts with sodium hydroxide (base) to produce sodium chloride (salt) and water.

HCl + NaOH → NaCl + H₂O

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Single Displacement Reaction

In these reactions, more reactive metal displaces less reactive metal from its salt.Reactivity series can be used to determine the products in these reactions. The reactivity series is a set of items grouped in decreasing order of reactivity. It indicates that the elements at the top of the reactivity scale are more reactive than those at the bottom. A single displacement reaction is the reaction of potassium with magnesium chloride. Because potassium is more reactive than magnesium, it displaces magnesium from its salt in this reaction. Potassium is the most reactive element and is found at the top of the reactivity scale.

2K + MgCl₂ → 2 KCl + Mg

Double Displacement Reaction

Two aqueous ionic compounds exchange their ions (mainly cations) and form two new compounds in these reactions. Potassium nitrate, for example, interacts with aluminium chloride to produce aluminium nitrate and potassium chloride.

KNO₃ + AlCl₃ → KCl + Al (NO₃)₃

Precipitation Reaction

These reactions result in the formation of an insoluble precipitate. Two soluble salts in aqueous solutions are joined in precipitation processes to generate an insoluble precipitate.

AgNO₃ _(aq) + KCl _(aq) → AgCl + KNO_{3 (aq)}

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Redox Reaction

Redox reactions are chemical reactions that involve both oxidation and reduction at the same time. The addition of oxygen is oxidation, while the addition of hydrogen is reduction (or removal of oxygen). A redox reaction is the reaction of copper oxide with hydrogen. In this reaction, hydrogen is oxidised by gaining one oxygen atom, whilst copper oxide is reduced by eliminating oxygen.

CuO + H₂ → Cu + H₂O

Types of Chemicals Reactions	General Reaction or Types of Chemical Equations:
Decomposition Reaction	AB → A + B
Combination Reaction	A + B → AB
Neutralization Reaction	Acid + base → Salt + Water
Combustion Reaction	A + O₂ → H₂O + CO₂
Displacement Reaction	A + BC → AC + B
Precipitation Reaction	A + B (soluble salt) → precipitate + C (soluble salt)

Difference Between Combination and Decomposition Reaction

Combination Reaction	Decomposition Reaction
Combination reactions occur when several reactants combine to produce a single product	Decomposition reactions occur when one reactant breaks down into numerous products.
2 Mg + O₂ → 2 MgO	2H₂O → 2H₂ + O₂

Synthesis Reaction

When two or more reactants combine to generate a single product, it is called a synthesis reaction. A + B → AB is a general equation that describes this type of reaction. The reaction of sodium (Na) and chlorine (Cl) to form sodium chloride (NaCl) is an example of a synthesis reaction.

Na + Cl → NaCl

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Frequently Asked Questions (FAQs)

1. A chemical equation is balanced on what basis?

A chemical equation is always balanced when the number of atoms of each element on the reactant and product sides are compared. It is based on the Law of Conservation of Mass, which states that the number of atoms on the left should equal the number on the right.

2. What is referred to as chemical change?

A chemical transition, also known as a chemical reaction, is a process that involves the transformation of one or more compounds into new and different substances. In other words, a chemical transformation is a chemical reaction that involves the rearrangement of atoms.

3. What is Redox Reaction?

An oxidation-reduction reaction is any chemical reaction in which, by obtaining or losing an electron, oxidation number of molecule, atom.

4. What are the signs of a chemical reaction?

Colour change, precipitate creation, gas generation, smell change, and temperature change are all examples of chemical reaction conditions.

5. Why is respiration considered an exothermic process?

An exothermic reaction is one in which energy is released. As energy is released during the process of respiration, it is referred to as an exothermic reaction.

6. How can you identify a combination reaction?

A combination reaction can be identified when two or more reactants combine to form a single product. The general equation is A + B → AB. For example, the reaction between hydrogen and oxygen to form water (2H₂ + O₂ → 2H₂O) is a combination reaction.

7. What distinguishes a decomposition reaction from other types?

A decomposition reaction is characterized by a single compound breaking down into two or more simpler substances. It's essentially the opposite of a combination reaction. The general equation is AB → A + B. For instance, the breakdown of water into hydrogen and oxygen (2H₂O → 2H₂ + O₂) is a decomposition reaction.

8. What is the difference between a synthesis reaction and a decomposition reaction?

A synthesis (or combination) reaction involves two or more reactants combining to form a single product (A + B → AB), while a decomposition reaction involves a single compound breaking down into two or more simpler substances (AB → A + B). They are essentially opposite processes.

9. What is the importance of stoichiometry in understanding chemical reactions?

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It's crucial for predicting the amounts of products formed, determining limiting reactants, and calculating reaction yields. Stoichiometric principles apply to all types of chemical reactions and are fundamental to chemical calculations.

10. How does the concept of limiting reactants apply to different types of chemical reactions?

The limiting reactant is the reactant that is completely consumed in a chemical reaction and determines the amount of product formed. This concept applies to all types of chemical reactions. Identifying the limiting reactant is crucial for calculating the theoretical yield of a reaction and understanding reaction stoichiometry.

11. What are the main types of chemical reactions?

The main types of chemical reactions are: combination (synthesis), decomposition, single displacement, double displacement, and combustion. Each type involves different arrangements of atoms or molecules to form new substances.

12. Can you explain what happens in a single displacement reaction?

In a single displacement reaction, one element replaces another element in a compound. The general form is A + BC → AC + B. An example is when zinc replaces hydrogen in hydrochloric acid: Zn + 2HCl → ZnCl₂ + H₂. The more reactive element (Zn) displaces the less reactive one (H).

13. What characterizes a combustion reaction?

A combustion reaction is a type of oxidation reaction where a substance reacts rapidly with oxygen, typically producing heat and light. It often involves a hydrocarbon reacting with oxygen to produce carbon dioxide and water. For example: CH₄ + 2O₂ → CO₂ + 2H₂O (methane combustion).

14. How does a double displacement reaction differ from a single displacement reaction?

A double displacement reaction involves the exchange of ions between two compounds, resulting in two new compounds. The general form is AB + CD → AD + CB. For example, when silver nitrate reacts with sodium chloride, we get silver chloride and sodium nitrate: AgNO₃ + NaCl → AgCl + NaNO₃.

15. Why is balancing chemical equations important in understanding reaction types?

Balancing chemical equations is crucial because it ensures that mass is conserved in the reaction (Law of Conservation of Mass). It helps in understanding the stoichiometry of the reaction, predicting the amounts of products formed, and identifying the type of reaction based on the number and nature of reactants and products.

16. What is the significance of the Law of Conservation of Mass in chemical reactions?

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. This principle is fundamental to understanding and balancing chemical equations. It ensures that the total mass of the reactants equals the total mass of the products, which is crucial for stoichiometric calculations and predicting reaction outcomes.

17. How do catalysts affect chemical reactions without being consumed?

Catalysts speed up chemical reactions by lowering the activation energy required for the reaction to occur. They do this without being consumed in the process. Catalysts provide an alternative reaction pathway with lower activation energy, allowing more reactant molecules to overcome the energy barrier and react. This principle applies to all types of reactions.

18. What role does energy play in different types of chemical reactions?

Energy plays a crucial role in chemical reactions. Endothermic reactions absorb energy from the surroundings, while exothermic reactions release energy. The energy changes can be in the form of heat, light, or electrical energy. Understanding these energy changes helps in classifying and predicting the behavior of different reaction types.

19. How can you determine if a reaction is exothermic or endothermic?

You can determine if a reaction is exothermic or endothermic by observing temperature changes or calculating the enthalpy change. If heat is released to the surroundings and the temperature increases, the reaction is exothermic. If heat is absorbed from the surroundings and the temperature decreases, the reaction is endothermic.

20. What is the role of oxidation numbers in redox reactions?

Oxidation numbers help identify which species are being oxidized (increase in oxidation number) or reduced (decrease in oxidation number) in a redox reaction. They aid in balancing redox equations and understanding electron transfer processes. Oxidation numbers can change in combustion, single displacement, and some double displacement reactions.

21. What is the importance of balancing redox reactions in acidic and basic media?

Balancing redox reactions in acidic and basic media is important because the medium can affect the half-reactions and overall reaction. In acidic media, H⁺ ions are often involved, while in basic media, OH⁻ ions play a role. Proper balancing ensures that mass and charge are conserved and helps in understanding the reaction mechanism in different environments.

22. How do coupled reactions relate to energy transfer in biological systems?

Coupled reactions involve linking an energetically unfavorable reaction with a favorable one, often seen in biological systems. For example, the hydrolysis of ATP is often coupled with energetically unfavorable processes. Understanding coupled reactions is crucial for comprehending energy transfer in living organisms and how different reaction types can be interconnected.

23. How do electrochemical reactions combine principles of redox reactions and electricity?

Electrochemical reactions involve the transfer of electrons through an external circuit, combining principles of redox reactions with electrical phenomena. These reactions are the basis of batteries and electrolysis processes. Understanding electrochemical reactions is crucial for applications in energy storage, corrosion prevention, and industrial processes.

24. What is the importance of reaction quotient in reversible reactions?

The reaction quotient (Q) is a measure of the relative amounts of products to reactants at any point in a reaction. It's crucial for understanding the direction of reversible reactions and how far they are from equilibrium. Comparing Q to the equilibrium constant (K) helps predict whether a reaction will proceed forward, reverse, or is at equilibrium.

25. How do solvent effects influence different types of chemical reactions?

Solvents can significantly affect reaction rates and equilibria by influencing the stability of reactants, products, and transition states. They can affect the polarity of the reaction environment, solvation of ions, and even participate in the reaction. Understanding solvent effects is crucial for predicting reaction outcomes and optimizing reaction conditions in various chemical processes.

26. What is the significance of Le Chatelier's Principle in reversible reactions?

Le Chatelier's Principle states that when a system at equilibrium is disturbed, it will shift to counteract the disturbance and establish a new equilibrium. This principle is crucial for predicting how changes in concentration, pressure, or temperature will affect the equilibrium position of reversible reactions. It's widely applied in industrial processes to optimize product yield.

27. How do pericyclic reactions differ from other organic reaction types?

Pericyclic reactions involve a cyclic transition state and a concerted rearrangement of electrons. They include reactions like Diels-Alder cycloadditions and electrocyclic reactions. Understanding pericyclic reactions is crucial in organic synthesis, as they allow for the formation of complex molecules in a single step, often with high stereoselectivity.

28. How can the activity series of metals help predict single displacement reactions?

The activity series of metals is a list of metals arranged in order of decreasing reactivity. It helps predict whether a single displacement reaction will occur. A more reactive metal can displace a less reactive metal from its compound. For example, zinc can displace copper from copper sulfate solution because zinc is more reactive than copper.

29. How do precipitation reactions relate to double displacement reactions?

Precipitation reactions are a subset of double displacement reactions where one of the products formed is an insoluble solid (precipitate). When two aqueous solutions are mixed and a precipitate forms, it's likely a double displacement reaction has occurred. For example: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq).

30. How do acid-base reactions fit into the classification of chemical reaction types?

Acid-base reactions are typically classified as double displacement reactions. They involve the transfer of protons (H⁺ ions) from an acid to a base. The general form is HA + BOH → BA + H₂O, where HA is an acid and BOH is a base. These reactions result in the formation of a salt and water.

31. What is the difference between a molecular equation and an ionic equation?

A molecular equation shows the complete formulas of all reactants and products in a reaction. An ionic equation shows the dissociated ions in solution, with spectator ions often canceled out to form a net ionic equation. Ionic equations are particularly useful for understanding precipitation and acid-base reactions.

32. What is the role of electron transfer in redox reactions?

In redox (reduction-oxidation) reactions, electron transfer occurs between species. The species losing electrons is oxidized, while the species gaining electrons is reduced. This electron transfer is fundamental to many types of reactions, including single displacement reactions, some double displacement reactions, and combustion reactions.

33. How do reversible reactions differ from irreversible reactions?

Reversible reactions can proceed in both forward and reverse directions, reaching a state of dynamic equilibrium. Irreversible reactions proceed only in the forward direction until the reactants are consumed. Understanding the reversibility of reactions is crucial for predicting reaction outcomes and understanding chemical equilibrium.

34. How do phase changes relate to chemical reactions?

While phase changes themselves are physical changes, they often accompany chemical reactions. For example, gas evolution in a decomposition reaction or precipitate formation in a double displacement reaction involves phase changes. Understanding these phase changes is important for fully characterizing reaction types and their observable effects.

35. What is the role of bond breaking and bond formation in chemical reactions?

Chemical reactions involve the breaking of bonds in reactants and the formation of new bonds in products. This process requires or releases energy, contributing to the overall enthalpy change of the reaction. Understanding bond breaking and formation is crucial for predicting reaction energetics and mechanisms across all reaction types.

36. How do combustion reactions relate to organic chemistry?

Combustion reactions are particularly important in organic chemistry, especially for hydrocarbons. The complete combustion of hydrocarbons produces carbon dioxide and water. Understanding these reactions is crucial for studying energy production, fuel efficiency, and environmental impacts. The general equation is: CxHy + O₂ → CO₂ + H₂O.

37. What is the significance of reaction rate in different types of chemical reactions?

Reaction rate, the speed at which reactants are converted to products, is important for all types of chemical reactions. Factors affecting reaction rates include concentration, temperature, surface area, and catalysts. Understanding reaction kinetics helps in optimizing industrial processes, predicting reaction outcomes, and studying reaction mechanisms.

38. How do photochemical reactions fit into the classification of reaction types?

Photochemical reactions are initiated by the absorption of light energy. They can be various types, including decomposition (e.g., photodissociation of water in photosynthesis) or combination reactions. Understanding photochemical reactions is crucial in fields like photosynthesis, photography, and atmospheric chemistry.

39. What is the role of intermediate species in complex reaction mechanisms?

Intermediate species are temporary products formed during a reaction that do not appear in the overall balanced equation. They are crucial in understanding reaction mechanisms, especially in organic and biochemical reactions. Identifying intermediates helps in breaking down complex reactions into simpler steps and understanding reaction pathways.

40. How do nuclear reactions differ from chemical reactions?

Nuclear reactions involve changes in the nucleus of atoms, while chemical reactions involve changes in the electron arrangements of atoms. Nuclear reactions can involve the transformation of elements, release much more energy than chemical reactions, and are not subject to the same chemical principles like the conservation of elements. Understanding these differences is crucial for distinguishing between chemical and nuclear processes.

41. What is the significance of activation energy in different types of chemical reactions?

Activation energy is the minimum energy required for a reaction to occur. It affects the rate of all types of chemical reactions. Reactions with lower activation energy proceed faster. Catalysts work by lowering the activation energy. Understanding activation energy is crucial for predicting reaction rates and designing reaction conditions in various chemical processes.

42. How do chain reactions differ from other types of chemical reactions?

Chain reactions involve a series of steps where the product of one step initiates another reaction step. They are self-propagating and can lead to exponential growth of product formation. Examples include polymerization reactions and nuclear fission. Understanding chain reactions is crucial in fields like polymer chemistry and nuclear physics.

43. What is the role of transition states in understanding reaction mechanisms?

Transition states represent the highest energy configuration of atoms during a reaction, occurring between the reactant and product states. They are crucial for understanding reaction pathways, activation energies, and the kinetics of all types of chemical reactions. Studying transition states helps in predicting reaction rates and designing more efficient chemical processes.

44. How do enzymes catalyze biochemical reactions?

Enzymes are biological catalysts that lower the activation energy of biochemical reactions without being consumed. They work by providing an alternative reaction pathway, often by stabilizing the transition state or bringing reactants together in a favorable orientation. Understanding enzyme catalysis is crucial for studying metabolic processes and developing pharmaceutical interventions.

45. What is the importance of reaction order in kinetics studies?

Reaction order describes how the rate of a reaction depends on the concentration of reactants. It's crucial for deriving rate laws and understanding reaction mechanisms. The overall order is the sum of the individual orders with respect to each reactant. Determining reaction order helps in predicting how changes in concentration will affect reaction rates.

46. How do free radical reactions differ from other types of reactions?

Free radical reactions involve species with unpaired electrons. They often proceed through chain reaction mechanisms and are important in organic synthesis, polymerization, and atmospheric chemistry. Free radicals can be highly reactive and understanding their behavior is crucial for predicting reaction outcomes and studying processes like oxidative stress in biological systems.

47. What is the role of resonance in understanding reaction mechanisms?

Resonance describes the delocalization of electrons in molecules, which can affect their stability and reactivity. Understanding resonance is crucial for predicting the behavior of compounds in various reaction types, especially in organic chemistry. It helps explain why some compounds are more stable or reactive than others, influencing reaction pathways and product distributions.

48. How do heterogeneous and homogeneous reactions differ?

Heterogeneous reactions occur between reactants in different phases (e.g., solid and liquid), while homogeneous reactions occur in a single phase. This distinction affects reaction rates, mechanisms, and how they are studied and applied. Understanding these differences is crucial for designing industrial processes, studying catalysis, and predicting reaction behaviors in various systems.

49. What is the significance of reaction yield in chemical synthesis?

Reaction yield is the amount of product obtained from a reaction compared to the theoretical maximum. It's crucial for assessing the efficiency of chemical processes, especially in industrial applications. Understanding factors affecting yield (like competing reactions, reversibility, or incomplete conversion) is important for optimizing reaction conditions and improving synthetic strategies.

50. What is the importance of understanding reaction mechanisms in drug design?

Understanding reaction mechanisms is crucial in drug design for predicting how drugs will interact with their targets, anticipating potential side effects, and designing more effective and selective drugs. It helps in optimizing synthetic routes for drug production and in understanding drug metabolism. This knowledge is fundamental to the development of new therapeutic agents.

51. How do substitution reactions differ in organic and inorganic chemistry?

In organic chemistry, substitution reactions typically involve the replacement of an atom or group with another, often following SN1 or SN2 mechanisms. In inorganic chemistry, substitution can involve ligand exchange in coordination compounds. Understanding these differences is crucial for predicting reaction outcomes and designing synthetic strategies in both fields.

52. What is the role of leaving groups in elimination and substitution reactions?

Leaving groups are atoms or molecules that depart during elimination or substitution reactions. The stability of the leaving group often determines the feasibility and rate of these reactions. Understanding leaving group effects is crucial for predicting reaction outcomes, especially in organic synthesis and biochemical processes.