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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.

(i) When the bulb starts glowing, its resistance increases due to the increase in temperature. Using Ohm's law,
R=V/I=4V/0.4A =10Ω
(ii) The reason for the difference in resistance is the phenomenon of electrical resistance increasing with temperature. When current flows through the bulb, it heats up, causing an increase in resistance.

Hazards of nuclear waste include:

1. Radioactive Contamination: Nuclear waste contains radioactive isotopes that emit harmful ionizing radiation, posing health risks to living organisms and the environment.
2. Long-term Storage: Nuclear waste remains hazardous for thousands of years and requires secure long-term storage facilities to prevent accidental exposure and contamination.
3. Nuclear Proliferation: Improper handling and disposal of nuclear waste can increase the risk of nuclear proliferation and the potential for nuclear accidents or terrorist attacks.

• Biodegradable substances are those that can be broken down into simpler substances by the action of microorganisms such as bacteria and fungi, leading to their decomposition and recycling in the environment. Non-biodegradable substances are those that cannot be broken down by natural processes and persist in the environment for a long time, causing pollution and environmental damage.