Notes of Class 10 Science Ch1 Chemical Reactions And Equations | NCERT Class 10

NCERT Class 10 Science Chapter 1 Overview

Chemical Reactions And Equations is the first chapter of chemistry class 10.In this chapter we are going to study about various types of chemical reactions such as comination reaction and displacement reaction.

Also, we have to study about Corrosion and Rancidity.

Notes of Physics Class 10 Ch 1 Chemical Reactions And Equations

1. Chemical Reaction

Chemical reactions are the reactions in which one or more new substances are formed during the reaction. This type of reaction is irreversible.
For Ex = Reaction of Magnesium with oxygen.

2. Chemical Equations

It is the representation of a chemical reaction in terms of symbols. Formulae of compounds are used instead of words in a chemical equation.
For Ex = N2(g) + 3H2(g) --> 2NH3(s) (Ammonia)

3. Balanced Chemical Equation

The chemical equation in which the number of atoms of various elements is the same on both sides of the arrow.
For Ex = CaCO3(s) (Calcium Carbonate) --> CaO(s) (Calcium Oxide) + CO2(g)

4. Skeletal Chemical Equation

The chemical equation in which the number of atoms of various elements is not the same on both sides of the arrow.
For Ex = 2Mg(s) + O2(g) --> 2MgO(s) (Magnesium Oxide)

5. Various Types of Chemical Equation

(i) Combination Reaction = It is a type of chemical reaction in which two or more substances combine to form a single compound.
For Ex = 2Mg(s) + O2(g) --> 2MgO(s)

(ii) Decomposition Reaction = It is a type of reaction in which a single substance breaks down to give two or more substances.

• Electrolysis/Electrolytic Decomposition = The decomposition reaction takes place only by passing electricity through the substance.For Ex = 2H2O(l) --> 2H2(g) + O2(g)
• Thermal Decomposition = The decomposition reaction that takes place only on heating the substance.For Ex = CaCO3(s) --> CaO(s) + CO2(g)
• Photochemical/Photolytic Decomposition = The decompostion reaction that takes place only by absorbing ligh energy.For Ex = 2AgCl(s) --> 2Ag(s) + Cl2(g)

(iii) Displacement Reaction = In this type of reaction, the more reactive element such as zinc displaces the less reactive element such as copper from its salt solution.
For Ex = Zn(s) + CuSO4(aq) --> ZnSO4(aq) + Cu(s)

(iv) Double Displacement Reaction = It is a type of chemical reaction in which two compounds react with each other two forms two different compounds by mutually(simultaneously) sharing the ions.
For Ex = Na2SO4(aq) + BaCl2(aq) --> NaCl(aq) + BaSO4(s)

(v) Precipitation Reaction = In this type of decomposition reaction, an insoluble solid known as a precipitate is formed. A precipitate substance is shown in the chemical equation followed by a down arrow.
For Ex = AgNO3(aq) + NaCl(aq) --> AgCl(s) + NaNO3(aq)

(vi) Neutralization Reaction = In this type of double displacement reaction, an acid reacts with a base to form their salt and water.
For Ex = HCl(aq) + NaOH(aq) --> NaCl(aq) + H2O(l)

(vii) Oxidation Reaction = It is a type of chemical reaction that involves the gain of oxygen or loss of hydrogen. Also, we can say that it involves a gain of electronegative element or loss of electropositive element.
For Ex = 2Cu(s) + O2(g) --> 2CuO(s)

(viii) Reduction Reaction = It is a type of reaction that involves the loss of oxygen or the gain of hydrogen. Also, we can say that it involves the loss of electronegative elements or the gain of the electropositive element.
For Ex = 2H2(g) + O2(g) --> 2H2O(l)

(ix) Redox Reaction = It is a type of chemical reaction that involves both oxidation and reduction reactions simultaneously.
For Ex = ZnO(s) + C(s) --> Zn(s) + CO(g)

(x) Exothermic Reaction = It is a type of chemical reaction in which heat energy is released or produced. To show heat is produced we write "+ heat" on the product side in a chemical reaction.
For Ex = C(s) + O2(g) --> CO2(g) + Heat

(xi) Endothermic Reaction = It is a type of chemical reaction in which heat energy is absorbed during the reaction. To show heat is absorbed we write "+ Heat" on the reactant side in a chemical reaction.
For Ex = CaCO3(s) + Heat --> CaO(s) + CO2(g)

6. Corrosion

The process of slowly eating up of metals due to their reaction with gases such as oxygen, water vapor, acids, etc. present in the atmosphere is known as corrosion.

For Ex = When Iron(Fe) reacts with oxygen and water it forms red substance known as 'Rust'.
2Fe(s) + 3/2 O2(g) + xH2O --> Fe2O3.xH2O (Rust) (Hydrated Iron Oxide)

Prevention = Corrosion can be prevented by following methods ->

• Painting, Galvanization, Oiling, Greasing.
• Corrosion of Aluminium(Al) has an advantage, since Aluminium Oxide(Al2O3) formed as a result of corrosion act as a protective layer.

7. Rancidity

The taste and smell of food containing oils or fats kept open in air for a long time changes because of rancidity. It is caused due to the oxidation of fats and oils of the food.
Prevention = Rancidity can be prevented by

• Adding anti-oxidants in the food, 
• Storing the food in an airtight container, and by flushing out air with nitrogen.
• Refrigeration of the food.

Conclusion

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