Class 10 Science Chapter 1 Notes Chemical Reactions & Equations

Class 10 Science Chapter 1 Notes Chemical Reactions and Equations

Chapter  1^st Chemical Reactions and Equations Notes

(1) Chemical Reaction

When a substance reacts with itself or any other substance to form a substance with one or more new chemical properties, then this is called a chemical reaction.

(2) Chemical Equation

Representation of a chemical reaction by the use of symbols and chemical formulae of reactants and products is called chemical reaction.

For example-

2Mg + O₂ → 2MgO

The substances which participate in chemical reaction are called reactants and the new substances obtained after chemical reaction are called products.

(3) Balanced Chemical Reaction

Number of all the atoms remains equal in the reactants and products of a balanced chemical equation. The chemical reaction must always be balanced which is done by hit or trial method.

(4) A complete chemical equation represents the reactants, products and their physical states symbolically.

(5) The gaseous, liquid, aqueous and solid states of reactants and products are represented by notations (g). (l), (aq) and (s), respectively.

(6) Following observations may occur during a Chemical Reaction-

(a) Change in state

(b) Change in colour

(c) Emission of a gas

(d) Change in temperature.

(7) Types of Chemical Reactions- Generally chemical reactions are of following type.

(i) Combination reaction– in a combination reaction two or more substances combine to form a new single substance.

For example-

CaO(s) + H₂O(l) → Ca(OH)₂ (aq) + Heat

C(s) + O₂(g) → CO₂(g)

(ii) Decomposition reaction– The reaction in which a single substance decomposes to give two or more substance is called decomposition reaction.

For example-

CaCO₃(s)  Heat →  CaO(s) + CO₂(g)

(iii) Displacement reaction- The reaction in which an element displaces another element from its compound is called displacement reaction.

For example-

Zn(s) + CuSO₄(s) → ZnSO₄ (aq) + Cu(s)

(iv) Double displacement reaction- The reaction in which two different atoms groups of atoms (ions) are exchanged, it is called double displacement reaction.

For example-

Na₂SO₄ (aq) + BaCl₂ (aq) → BaSO₄(s) + 2NaCl(aq)

(v) Oxidation and Reduction- in a reaction gain of oxygen or loss of hydrogen is called oxidation. The process of reduction is opposite to oxidation in which loss of oxygen or gain of hydrogen occurs.

For example-

Oxidation- 2Cu + O₂  Temperature →2CuO (Gain of Oxygen)

Reduction- CuO + H₂  Temperature → Cu + H₂O (Gain of Hydrogen)

(vi) Redox reaction- The chemical reactions in which oxidation and reduction reactions occur simultaneously are called redox reactions.

For example-

CuO + H₂ →   Cu + H₂O

Oxidation- H₂ → H₂O

Reduction- CuO → Cu

(vii) Precipitation reaction– The reactions in which a insoluble substance (precipitate) is formed are called precipitation reactions.

For example-

NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)

(8) On the basis of heat, reactions are classified in two parts.

(a) Exothermic reaction- Reactions in which heat is given out along with the products are called exothermic reactions.

For example- CH₄(g)+2O₂(g) → CO₂(g) + 2H₂O(g) + Energy

(b) Endothermic reaction- Reactions in which energy is absorbed are known as endothermic reactions.

For example- 2AgCl(s)  Sunlight→ 2Ag(s) + Cl₂(g)

(9) Corrosion- When a metal comes in contact with acid, base or moisture then it will corrode. This process is called corrosion.

(10) Rancidity– When fats and oils are left for a long time then taste and odour of these have changed due to oxidation. This is called rancidity.

Class 10 Science Chapter 1 Notes pdf

Science is a subject that explains how the world around us is formed and how things happen because of the chemical reactions that take place around us. From corrosion to decomposition, chemical reactions provide a more in-depth understanding of how molecular interactions and changes occur. CBSE Class 10 Science Chapter 1 explains how matter changes form. Click Here to Download in PDF format.