Chemical Reactions and Equations of Class 10th Science

Chapter 1 - Chemical Reactions and Equations of Class 10th Science

Topics in the Chapter

• Introduction
• Chemical reaction
• Chemical equation
• Balanced chemical equation
• Types of chemical reaction
• Corrosion
• Rancidity

Introduction

→ Most of the substance around us undergoes various changes. Some of these changes are temporary with no new substance being formed. They are called physical changes.

→ In certain other changes the new substance formed in which the reactant or the parent loses its identity to form new substance called product. These changes are permanent changes as we won’t get the reactant back.

Chemical Reaction

→ Chemical reaction is the process by which two or more substance react with each other to form new substance with different properties.

→ These are the following changes to determine that the chemical reaction has taken place:
(i) Change in state
(ii) Change in colour
(iii) Evolution of gas
(iv) Change in temperature

Chemical Equation

→ A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formulae, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side.

Magnesium + oxygen → magnesium oxide

(Reactant) (Product)

Balanced chemical equation

→ The chemical equation that shows the chemical reaction needs to be balanced. A balanced chemical equation occurs when the number of the atoms involved in the reactants side is equal to the number of atoms in the products side.

Zn + H₂SO₄ → ZnSO₄ + H₂
3Fe (s) + 4H₂O(g) → Fe₃O₄ (s) + 4H₂ (g)

Types of chemical reaction

→ Combination reaction: Two or more substances combine to form a single product.

CaO (s) + H₂O (l) → Ca(OH)₂ (aq)

Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃(s) + H₂O (l)
(slaked lime) (calcium carbonate)

Burning of coal: C (s) + O₂ (g) → CO₂(aq)
Formation of water: H₂ (g) + O₂ (g) → H₂O (aq)
Burning of natural gas (Methane): CH₄ (g) + O₂ (g) → CO₂ (g) + H₂O (l)

→ Exothermic reaction: An exothermic reaction is a chemical reaction that releases energy in the form of heat or light.

C₆H₁₂O₆ (aq) + 6O₂ (aq) → 6CO₂ + 6H₂O (l) + energy
(glucose)

→ Endothermic reaction: An endothermic process absorbs heat and cools the surroundings.

→ Decomposition reaction: A single reactant breaks down to yield two or more products.

· Thermal decomposition: 2Pb(NO₂)₂ → 2PbO + 4NO₂ + O₂

· Electrolysis: 2H20 → 2H₂ + O₂

· Photochemical reaction: 2AgBr → 2Ag + Br₂

→ Displacement reaction: An element displaces another element from its compound.

Fe (s) + CuSO₄ (aq) → FeSO₄ (g) + Cu (s)
Pb (s) + CuCl₂ (aq) → PbCl₂ (aq) + Cu (s)

→ Double Displacement reaction: Exchange of ions takes place between two compounds.

Na₂(SO)₄ (aq) + BaCl₂ (aq) → BaSO₄ (s) + NaCl (aq)

→ Redox reaction:

· Redox reactions involve the transfer of electrons from one substance to another.

· Oxidation is the loss of electrons or an increase in oxidation state.

· Reduction is the gain of electrons or a decrease in oxidation state.

ZnO + C → Zn + CO
ZnO is reduced to Zn—reduction. C is oxidized to CO—Oxidation.

→ Oxidizing Agent

It is the substance which gives oxygen or gains hydrogen.
Or it the substance which is reduced itself and oxidizes other.

→ Reducing Agent

It is the substance which gives hydrogen or gains oxygen.
Or it the substance which is oxidized itself and reduces other.

Effects of Oxidation Reactions in Our Daily Life:

Corrosion: Corrosion is the gradual destruction of metals due to their reaction with oxygen and moisture in the environment.

· Common examples of corrosion include the rusting of iron and tarnishing of silver.

Corrosion (rusting) of Iron: Fe2O3. nH2O (Hydrated iron oxide)

Rancidity: Rancidity is the process in which fats and oils present in food items become rancid due to oxidation.

· It results in an unpleasant odor and taste.

Preventive methods of rancidity: - Adding antioxidants to the food materials, storing food in the airtight container, flushing out air with nitrogen gas and refrigeration.

· To prevent rancidity, store food in airtight containers and avoid exposure to light and heat.