Learn Science with Free Lessons & Tips

Types of Chemical Reactions

1. Combination Reaction

When two or more substances combine to form a single product, the reaction is known as a combination reaction.

For example:

In the laboratory, iron sulphide is prepared by mixing iron and sulphur.

Fe_(s) + S_(s) → FeS(s)

Formation of slaked lime by the reaction of calcium oxide with water

• Endothermic Reaction: The reactions accompanied by the absorption of heat are called endothermic reactions.
• Exothermic Reaction: The reactions accompanied by the evolution of heat are called endothermic reactions.

1.   Decomposition Reaction

A chemical reaction in which a single compound splits into two or more simple substances is called a decomposition reaction.

Correct way of heating the boiling tube containing crystals of ferrous sulphate and of smelling the odour

For example:

When mercuric oxide is heated in a crucible, the orange-red powder begins to darken and a silver mirror begins to deposit on the cooler parts of the crucible.

• Thermal Decomposition Reaction: The decomposition reactions carried out by heating are known as thermal decomposition reactions.
• Photochemical reaction: The chemical reactions which proceed with the absorption of light energy are called photochemical reactions.

2.               Displacement Reaction

Reactions in which the more reactive element displaces the less reactive element from its compound are called displacement reactions.

Iron nails dipped in copper sulphate solution

For example:

Zinc displaces copper in copper sulphate to form zinc sulphate. 

1.   Double Displacement Reaction

Reactions in which ions of the reactants exchange places to form two new compounds, are called double displacement reactions.

For example: Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.

NaOH_(aq)          +          HCl_(aq)   →       NaCl_(aq) +          H2O_(l)

Types of Double Displacement Reactions: 

1. Precipitation 

In all of the following processes, a white material is generated that is insoluble in water. A precipitate is the insoluble substance that forms. A precipitation reaction is a reaction that results in the formation of a precipitate.

1. Neutralization 

The reactants are a base and an acid, and the products are salt and water. Neutralization is a form of double displacement reaction in which the reactants are a base and an acid, and the products are salt and water. The positive charge of the acid's hydrogen ion and the negative charge of the base's hydroxyl ions or oxide ions lose their electrical charge and form covalent water molecules. 

Na⁺OH^- + H⁺Cl^-        →      Na⁺Cl^- + H₂O

Base     Acid                   Salt    Water

Zn₂+O₂- + 2H+NO₃^- → Zn₂⁺(NO₃)₂^- + H₂O

A neutralization reaction is basically a reaction between H+ and OHions i.e., 

H⁺_(aq) + OH^-_(aq) → H₂O_(l)

2.               Oxidation - Reduction Reactions/Redox Reactions

Oxidation and reduction take place simultaneously.

Reactions which involve the addition of oxygen, or the removal of hydrogen are called oxidation reactions. For example:

Zinc displaces copper in copper sulphate to form zinc sulphate. 

1.   Double Displacement Reaction

Reactions in which ions of the reactants exchange places to form two new compounds, are called double displacement reactions.

For example: Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.

NaOH_(aq)          +          HCl_(aq)   →       NaCl_(aq) +          H2O_(l)

Types of Double Displacement Reactions: 

1. Precipitation 

In all of the following processes, a white material is generated that is insoluble in water. A precipitate is the insoluble substance that forms. A precipitation reaction is a reaction that results in the formation of a precipitate.

1. Neutralization 

The reactants are a base and an acid, and the products are salt and water. Neutralization is a form of double displacement reaction in which the reactants are a base and an acid, and the products are salt and water. The positive charge of the acid's hydrogen ion and the negative charge of the base's hydroxyl ions or oxide ions lose their electrical charge and form covalent water molecules. 

Na⁺OH^- + H⁺Cl^-        →      Na⁺Cl^- + H₂O

Base     Acid                   Salt    Water

Zn₂+O₂- + 2H+NO₃^- → Zn₂⁺(NO₃)₂^- + H₂O

A neutralization reaction is basically a reaction between H+ and OHions i.e., 

H⁺_(aq) + OH^-_(aq) → H₂O_(l)

2.               Oxidation - Reduction Reactions/Redox Reactions

Oxidation and reduction take place simultaneously.

Reactions which involve the addition of oxygen, or the removal of hydrogen are called oxidation reactions. For example:

C_(s) + 2H_{2 (g)} → CH_{4 (g)}

Chemical reactions in which the reactants gain hydrogen are reduction reactions. For example:

·       Oxidation: Substance loses electrons or gains oxygen or loses hydrogen.

·       Reduction: Substance gains electrons or loses oxygen or gains hydrogen.

·       Oxidising agent: a substance that oxidises another substance and self-gets reduced.

·       Reducing agent: a substance that reduces another substance and self-gets oxidised.

Redox Reaction

The chemical reaction in which oxidation and reduction takes  places simultaneously is known as a redox reaction.

When we see any object through hot air over the fire, it appears wavy and slightly moving due to the phenomenon of atmospheric refraction. The hot air above the fire has different refractive indices due to temperature variations, causing light passing through it to bend and creating a distorted image.

The resistance of the bulb can be calculated using Ohm's law: R=V/I=330V/110W=3Ω The energy consumed by three bulbs burning for 5 hours is E=P⋅t=110W×3×5h=1650Wh=1.65kWh The cost in rupees is calculated as Cost=Energy consumed×Rate=1.65kWh×0.70 Rupees/kWh=1.155

The resistance of the copper wire can be calculated using the formula R=ρ⋅l/A, where ρρ is the resistivity of copper, ll is the length of the wire, and AA is the cross-sectional area of the wire. Given ρ=1.72×10−8 Ω⋅mρ=1.72×10−8Ω⋅m, l=2 km=2000 ml=2km=2000m, and r=2 mm=0.002 mr=2mm=0.002m (radius),the cross-sectional area A=πr2=π×(0.002)2 m2A=πr2=π×(0.002)2m2. Substituting these values into the formula gives R=(1.72×10−8 Ω⋅m)×(2000 m)π×(0.002)2 m2R=π×(0.002)2m2(1.72×10−8Ω⋅m)×(2000m). Calculating this expression gives the resistance of the wire.

Biogas is considered to be a boon to farmers for several reasons:

1. Energy Production: Biogas provides a renewable source of energy for farmers, which can be used for cooking, heating, and lighting purposes. This reduces their reliance on traditional sources of fuel like wood, dung, or fossil fuels, thereby saving costs and reducing environmental impact.

2. Waste Management: Biogas production involves the anaerobic digestion of organic waste materials such as animal dung, crop residues, and kitchen waste. By converting these waste materials into biogas, farmers can effectively manage and dispose of organic waste while simultaneously producing energy.

3. Fertilizer Production: The byproduct of biogas production, known as digestate, is a nutrient-rich fertilizer. Farmers can use digestate to improve soil fertility and enhance crop yields, reducing the need for chemical fertilizers and promoting sustainable agriculture practices.

• Bad ozone refers to ozone molecules present in the lower atmosphere, also known as ground-level ozone. It is considered "bad" because it is a harmful air pollutant that can cause respiratory problems and damage to vegetation and ecosystems.
• Natural ecosystems are those that occur and develop without human intervention, such as forests, grasslands, and wetlands. Artificial ecosystems, also known as human-made or anthropogenic ecosystems, are deliberately created or modified by humans for specific purposes, such as agricultural fields, urban parks, and gardens.