CLASS 10 NCERT SCIENCE SHORT NOTES IN ENGLISH

Chemical reaction :- Such changes in which substances with new properties are formed are called chemical reactions. Examples:- Digestion of food, respiration, rusting of iron, burning of magnesium ribbon, making of curd etc.

These factors show that a chemical reaction has taken place:- Change in state of substance, Change in color of substance, Evolution of heat, Absorption of heat, Evolution of gas, Evolution of light.

Reactant :- Substances which take part in a chemical reaction are called reactants.

Product :- Such substances which are formed in chemical reaction are called products.

Chemical Equation :- A brief representation of a chemical reaction through symbols and formulas of the substances taking part in it (reactant and product) is called chemical equation.

Chemical reactions are represented by chemical equations. In a chemical equation, the symbols of the elements or the chemical formulas of the reactants and products are written along with their physical states. In a chemical reaction, the necessary conditions like temperature, pressure, catalyst etc. are shown above or below the arrow mark.

Balanced Chemical Equation :- Such a chemical equation in which the number of atoms of each element is equal on both the sides (left and right sides), is called balanced chemical equation.

Law of Conservation of Mass :- In any chemical reaction, mass is neither created nor destroyed. The number of atoms of each element before the chemical reaction (reactant) and after it (product) should be the same.

To Chemical Equations Balancing (Hit and Trial Method) :-

Phase 1 :- After writing chemical equations, make a box around each formula.

Fe + HO FeO + H

Do not change anything inside the box while balancing.

Phase 2 :- Note the number of atoms of different elements present in the equation. Elements Number of atoms in reactants (LHS) Number of atoms in products (RHS)

Fe 1 3

H 2 2

O 1 4

step 3 :- Balance the element with highest number of atoms by applying improper coefficient on the reactant or product side.

Fe +4 HO FeO + 4 H

step 4 :- Balance the atoms of all the elements as in step 3.

3 Fe + 4 HO FeO + 4 H

The number of atoms of all the elements is equal on both sides of the reaction.

Step 5 :- Writing the physical state of reactants and products :-

Solid :- ( s ) Liquid :- ( l ) Gaseous state :- ( g ) Aqueous solution :- ( aq )

3Fe(s) + 4HO( g ) FeO + 4H( g )

Step 6 :- Write some necessary conditions like: temperature, pressure or catalyst etc. above or below the arrow mark. The number of atoms of the elements on both sides of the equation is equal. Hence this equation is now balanced.

This method of balancing chemical equations is called hit and trial method because we try to balance the equation by using the coefficient of the smallest integer number.

Dettagli