CBSE Class 10 Science Chapter 1 - Chemical Reactions and Equations

Class Notes of Ch 1: Chemical Reaction and Equations 
Class 10th Science

Chemical Reactions and Equations

Topics:

• Introduction 
• Chemical Reaction 
• Chemical Equation
• Balanced Chemical Reaction
• Corrosion
• Rancidity

Introduction

• Most of the substance in nature that undergoes various changes. Some of these changes are temporary with no new substance being formed. These changes are called Physical Changes.

• In other change, anew substance is formed, in which the reactant loses its identity to form a new substance called product. These are permanent changes because we can not get the reactant back.

Chemical Reaction

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

• The following observations helps us to determine whether a 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 formulas, where the reactant entitles are given on left-hand side  and the product entitles 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 reactant side is equal to the number of atoms in the product side.

Zn + H₂SO₄ = ZnSO₄ + H₂

3Fe (s) + 4H_{2O(g) =Fe3O (s)+4H2 (g)}

_{Types of Chemical Reaction}

• Combination Reaction: Such a reaction in which a single product is formed from two or more reactants is known as a combination reaction.

          CaO(s) + H₂O(l) = Ca(OH)₂(aq)

         Calcium oxide reacts vigouosly with water to produce slaked lime (calcium hydroxide)           releasing a large amount of heat.

         A solution of slaked lime produced by the reaction is used for white washing walls. Calcium hydroxide reacts slowly with the carbon dioxide in the air to form a thin layer of calcium carbonate on the walls. It is interesting to note that the chemical formula for marble is also CaCO_3.

_{Ca(OH)2  (aq)+}CO_{2(g)  →} CaCO_{3 (s) +} H2O (l)

 (salked lime)                        (calcium carbonate)

• Endothermic Reaction: An exothermic process releases heat and causes the temperature of the immediate surroundings to rise. the rice, potato and bread we eat contains carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. The special name of this reaction is respiration is an exothermic reaction.   

          12 FeSO4 (s) = 6 Fe2O3  (g)+ S02 (g) + 10 SO3 (g)

 (Ferrous Sulphate)     (Ferric Oxide)    

2Pb(NO2)3 = 2PbO +4NO2 +O2

(lead nitrate)             (lead oxide)

White silver chloride turns grey in sunlight. this is due to the decomposition of silver chloride into silver and chlorine by light.

2AgCl(s) = 2Ag9s) +Cl2(g)

2AgBr(s)= 2Ag(s)+Br2(g)

• Displacement Reaction: Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals & non-metals take part in displacement reactions. Reaction of iron nails with copper sulphate solution.

          Fe + CuSo₄ = FeSo₄ + Cu

          Pb + CuCl₂ = PbCl₂ + Cu

• Double Displacement Reaction: A double displacement reaction is a type of chemical reaction where two compounds react and the positive ions of the two reactant switch places forming two new compounds or product.

          BaCl₂ + Na₂So₄ = BaSo₄ + 2 NaCl

• Redox Reaction: An oxidation-reduction (Redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation=reduction number of a molecule, atom or ion changes by gaining or losing an electron.

         Oxidation: This process involves gain of oxygen or loss of hydrogen.

         Reduction: This process involves the gain of  hydrogen or loss of oxygen.

           CuO + H₂ = Cu + H₂O

• Oxidizing Agent: It is the substance which gives oxygen or gains hydrogen or the substance which is reduced itself and oxidized other.

• Reducing Agent: It is the substance which gives hydrogen or gains oxygen or the substance which is oxidized itself and reduces other. Oxidation is the process which involves loss of electrons but the reduction is the process which involves gain of electrons.

Corrosion

The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen, water, acids, gases etc. present in the atmosphere is called corrosion.

Rusting: Iron when reacts with oxygen and moisture forms red substance calles rust.

Rancidity

• The taste and odor of food materials containing fat and oil changes when they are left exposed to air for a long time. This called rancidity. It is caused due to oxidation of fat and oil present in food material.
• It can be prevented by using various methods such as by adding antioxidants to the food material, storing food in air tight container and by flushing out air with nitrogen.

Also Read :

SCIENCE Revision Notes

Chapter:01  Chemical Reaction & Equation
Chapter:02  Acid Base & Salt
Chapter:03  Metals & Non Metals
Chapter:04  Carbon & its Components
Chapter:05  Periodic Classification of Elements
Chapter:06  Life Processes
Chapter:07  Control & Coordinates
Chapter:08  How do Organisms Reproduce
Chapter:09  Heridity & Evolution
Chapter:10  Light Reflection Refraction
Chapter:11  The Human Eye & the Colourful World
Chapter:12  Electricity
Chapter:13  Magnetic Effect of Electric Current
Chapter:14  Source Of Energy
Chapter:15  Our Environment
Chapter:16  Management of Natural Resource

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