Short Notes -Class10-Chemistry- Chapter 1 – Chemical Reaction and Equation

Class 10 – Science -Chemistry -Short Notes -Chapter 1 – Chemical Reaction and Equation

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 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.

Irreversible changes often involve chemical reactions, as opposed to physical changes, which can be reversible.

Chemical reactions: A chemical reaction is a process in which new substances (products) with different properties are formed as a result of the breaking of bonds in reactants.

These are the following changes to determine that the Chemical reaction has taken place

1. Change in state
2. Change in colour
3. Evolution of gas
4. Change in temperature  

Chemical equation: A chemical equation is a symbolic representation of a chemical reaction where the reactants and the products are shown by their symbols or formulas.

It includes reactants on the left side, an arrow to indicate the direction of the reaction, and products on the right side.

The coefficients in the equation represent the mole ratios of the reactants and products.

For example:

     Na        +       Cl         →         NaCl

(Sodium)     (Chlorine)    (Sodium chloride)

Balancing chemical equation:

The chemical equation in which the number of atoms of each element in the reactants side is equal to that of the products side is called a balanced chemical equation.

Balancing is essential to ensure that the law of conservation of mass is followed. This law states that the total mass of reactants must be equal to the total mass of products in a chemical reaction.

Balancing involves adjusting coefficients to make the number of atoms of each element the same on both sides of the equation.

Short Technique for Balancing a Chemical Equation

Let us take the same chemical reaction and try to balance it using a short technique which will save your time and effort in the exam. Let the number of molecules on each side be,

aKMnO4+ bHCl → cKCl + dMnCl2 + eH2O + fCl2

Now comparing LHS and RHS,

K: a = c

Mn: a = d

O: 4a = e

H: b = 2e

Cl: b = c + 2d + 2f

Let us take a = 2, then

c = d = a = 2

b = 2e = 8a = 16

So, e = 8

So, 16 = 2 + 2(2) + 2(f)

f = 5

Thus, the required equation is: 2KMnO4+ 16HCl → 2KCl + 2MnCl2 + 8H2O + 5Cl2.

From a chemical equation we can conclude:

• Various reactants and products’ names
• Reactant and product formulae
• The number of moles of the reactants and products in relation to each other
• Masses of reactants and products relative to each other
• Volumes of gaseous reactants and products in relation to each other.