Question

explain explain science to first lesson of 10th standard full

Answer 1

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: 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 vigorously 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 air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls. It is interesting to note that the chemical formula for marble is also CaCO3.
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 process releases heat, and causes the temperature of the immediate surroundings to rise The rice, potatoes and bread we eat contain 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.

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

→ Endothermic reaction: An endothermic process absorbs heat and cools the surroundings.
The decomposition of vegetable matter into compost is also an example of an endothermic reaction.

→ Decomposition reaction: When single reactant breaks down to give simpler products. This is a decomposition reaction.

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

The above reactions are used in black and white photography.

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

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

→ Double Displacement reaction: A double displacement reaction, also known as a double replacement reaction or metathesis, is a type of chemical reaction where two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming t