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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.

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.

• Domestic appliances typically use parallel connections. This is because in parallel connections, each appliance gets the full voltage of the power supply, ensuring consistent operation regardless of the other appliances in the circuit. Additionally, if one appliance fails or is turned off, it does not affect the operation of other appliances connected in parallel.

a. When the magnitude of electric current in the wire is increased, the compass needle deflects more, showing a stronger magnetic field around the wire. b. The compass needle is deflected away from the wire because the direction of the magnetic field produced by the current in the wire is opposite to the direction of the magnetic field of the compass needle.

A solar cell panel, also known as a photovoltaic (PV) panel, is a device that converts sunlight directly into electricity using the photovoltaic effect. Three applications of solar cell panels are:

1. Residential and Commercial Solar Power Systems: Solar panels can be installed on rooftops of homes, buildings, and offices to generate electricity for on-site consumption or to feed excess power back into the grid.

2. Off-grid Power Solutions: Solar panels are used in remote areas or locations where access to traditional power grids is limited or unavailable. They provide a reliable source of electricity for powering remote homes, telecommunications equipment, water pumps, and other applications.

3. Solar-powered Gadgets and Appliances: Solar panels are used to power various gadgets and appliances such as calculators, street lights, outdoor lighting, solar-powered chargers, and solar-powered water heaters.

• Plastic bags are non-biodegradable because they are made from synthetic polymers such as polyethylene, polypropylene, and polyethylene terephthalate (PET), which are resistant to microbial degradation. This means that plastic bags persist in the environment for a long time, contributing to pollution and environmental damage.