Types of Chemical Reactions

A chemical reaction is a transformative process where reactants change, forming new products. This transformation involves the movement of electrons, the breaking of existing bonds, and the formation of new bonds, resulting in the creation of desired products and sometimes by-products. Chemistry revolves around the interactions between elements and compounds, specifically through bonds and reactions.

• There are mainly 8 types of chemical reactions.
• The types of chemical reactions are based its characteristics.
• Some common types of reactions are Combination reaction, Decomposition reaction, Displacement reaction and Double displacement reaction.

Key Terms-: Chemical Reaction, Decomposition, Combination, Combustion, Neutralization, Single Displacement, Double Displacement, Precipitation, Redox.

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What is Chemical Reaction?

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A chemical reaction is a process where two or more elements or compounds interact with each other, leading to the formation of a product. The substances involved in the reaction are referred to as reactants.

 

• In a chemical reaction, bonds between atoms are broken and new bonds are formed, resulting in the formation of the desired product.
• The rate at which a chemical reaction occurs is known as the rate of reaction.
• It depends on various factors such as the concentration of reactants, pressure, and temperature. 
• As a result of the chemical reaction, the original properties of the reactants change, leading to the formation of products with different properties.

Read More: Oxides of Nitrogen

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Characteristics of a Chemical Reaction 

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Some characteristics of Chemical Reaction are mentioned below:

Evolution of Gas

Certain chemical reactions result in the release of gas. For instance, when zinc reacts with hydrochloric acid, hydrogen gas is produced as a byproduct, while zinc chloride is formed.

• Reaction- Zn + 2HCl → ZnCl₂ + H₂

Change in Colour 

Certain chemical reactions are characterized by a noticeable change in color. For instance, when a colorless substance like lead nitrate reacts with potassium iodide, it results in the formation of a yellow precipitate of lead iodide and colorless potassium nitrate.

• Reaction- Pb(NO₃)₂ + 2KI → PbI₂ + 2KNO₃

Change in Temperature

 

Certain chemical reactions are accompanied by temperature changes. For instance, some reactions release heat, known as exothermic reactions, while others absorb heat, known as endothermic reactions.

Change in Energy 

Chemical reactions frequently involve an alteration in energy. In the course of a chemical reaction, energy can either be released or absorbed. For instance, in combustion reactions, energy is liberated through processes like the burning of fuel.

Formation of Precipitate 

Certain chemical reactions result in the formation of a precipitate. One such example is the reaction between barium chloride and sodium sulfate, which leads to the formation of sodium chloride and a precipitate of barium sulfate.

• Reaction- BaCl₂ + Na₂SO₄ → BaSO₄ + NaCl

Change in State 

Certain chemical reactions involve a transition in the physical state of substances. One such example is the reaction between ammonia gas and hydrogen chloride gas, which results in the formation of solid ammonium chloride crystals.

• Reaction- NH₃(g) + HCl(g) → NH₄Cl(s)

Read More: Difference Between Oxidation and Reduction

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Types of Chemical Reactions 

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Here are the types of Chemical Reactions:

Combination Reaction 

A combination reaction is a type of chemical reaction where two or more substances combine to form a new substance. 

• This is also known as a synthesis reaction. 
• In a combination reaction, the reactants are typically elements or simple compounds, and the product is a more complex compound.
• Reaction- Mg + O₂ → MgO

In the following reaction, sodium undergoes a reaction with chlorine to produce sodium chloride as the resulting product.

2Na(s) + Cl₂(g) → 2NaCl(s)

Decomposition Reaction 

A decomposition reaction is a chemical reaction in which one reactant breaks down into two or more products. 

• This can happen when the reactant is heated, exposed to light, or passed through an electric current.
• For example, when water is decomposed by electrolysis, it breaks down into hydrogen and oxygen gas. 
• This reaction can be represented by the following equation:

Reaction - 2H₂O electricity → 2H₂ + O₂

• In the below reaction, calcium carbonate is decomposed and forms calcium carbonate and carbon dioxide in gaseous form.

CaCO₃ → CaO + CO₂

Read More: Electrochemical Cells

Combustion Reaction 

Combustion is a chemical reaction that occurs when a fuel reacts with oxygen to produce heat and light. 

• The fuel is typically a hydrocarbon, which is a compound made up of carbon and hydrogen. 
• When a hydrocarbon burns, the carbon and hydrogen atoms in the fuel react with oxygen atoms in the air to form carbon dioxide and water. 
• This reaction releases a large amount of energy, which is why combustion is used to power cars, stoves, and other devices.

Reaction- CH₄ + 2O₂ → CO₂ + 2H₂O

Neutralisation Reaction 

A neutralisation reaction is a chemical reaction between an acid and a base. When an acid and a base react, they neutralise each other, meaning that they cancel out each other's properties. 

• Acids are sour and have a pH below 7, while bases are bitter and have a pH above 7.
• When an acid and a base react, they produce salt and water. 
• The salt is a neutral substance, meaning that it has a pH of 7.

An example of a commonly observed neutralisation reaction involves the interaction between hydrochloric acid, a strong acid, and sodium hydroxide, a strong base.

HCl + NaOH → NaCl + H₂O

Single Displacement Reaction 

A single displacement reaction is a chemical reaction in which one element replaces another element in a compound. 

• This happens when the element that is being replaced is less reactive than the element that is doing the replacing. 
• For example, if you put a piece of zinc in a solution of copper sulfate.
• The zinc will replace the copper in the solution, forming zinc sulfate and copper metal.

Zn + CuSO₄ → ZnSO₄ + Cu

An illustration of this type of reaction is the reaction between potassium and magnesium chloride, which is a single displacement reaction. 

• In this reaction, potassium displaces magnesium from its salt because potassium is more reactive than magnesium. 
• Potassium, being at the top of the reactivity series, is the most reactive element.

2K + MgCl₂ → 2KCl + Mg

Double displacement reaction 

A double displacement reaction is a type of chemical reaction in which two compounds exchange their ions to form two new compounds. This type of reaction is often called a "salt metathesis reaction" or a "double decomposition reaction."

KNO₃ + AlCl₃ ↔ Al(NO₃)₃ + KCl

Precipitation Reaction 

A precipitation reaction is a chemical reaction that occurs when two solutions are mixed and one of the products is an insoluble solid, called a precipitate. The precipitate is formed when the ions in the two solutions combine to form an insoluble compound.

• The typical precipitation reactions that occur in an aqueous solution involve the creation of an insoluble ionic compound 
• When two solutions containing soluble compounds are combined. 
• For example, when an aqueous solution of NaCl is mixed with an aqueous solution of AgNO₃. 
• The first solution contains hydrated Na⁺ and Cl⁻ ions, while the second solution contains Ag⁺ and NO₃⁻ ions.

1.  NaCl(s) → Na⁺(aq) + Cl⁻(aq)
2. AgNO₃(s) → Ag⁺(aq) + NO₃⁻(aq)

Redox Reaction 

In a redox reaction, one reactant is oxidized and the other reactant is reduced.The oxidized reactant loses electrons and becomes more positively charged, while the reduced reactant gains electrons and becomes more negatively charged.

• An example of a redox reaction is the reaction between copper oxide and hydrogen. 
• In this reaction, hydrogen undergoes oxidation by gaining oxygen atoms, while copper oxide undergoes reduction by losing oxygen atoms.

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Things To Remember

• In a synthesis reaction, two or more substances combine to form a new compound.
• A decomposition reaction is the opposite of synthesis, where a compound breaks down into simpler substances.
• Combustion reactions involve a substance reacting with oxygen to produce heat and light, often resulting in the formation of carbon dioxide and water.
• In an acid-base reaction, an acid and a base react to form salt and water.
• Oxidation-reduction (redox) reactions involve the transfer of electrons from one substance to another.
• Precipitation reactions occur when two solutions react to form a solid substance called a precipitate.
• In a displacement reaction, an element in a compound is replaced by another element.
• A neutralization reaction happens when an acid and a base react to neutralize each other and form salt and water.
• In a double displacement reaction, the positive and negative ions of two compounds switch places to form new compounds.