The process in which new substances with new properties are formed from one or more substances is called chemical.
Reaction.
Substances that participate in a chemical reaction are called reactants.
Substances formed during a chemical reaction are called products.
Examples:
(i) Digestion of food
(ii) Breathing
(iii) Iron rust
(iv) Burning the magnesium ribbon
(v) Curd formation
Example: MgO.

Characteristics of chemical reactions:
(i) Evolution of gas: The chemical reaction between zinc and dilute sulfuric acid is characterized by the evolution of hydrogen gas.
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) ↑

(ii) Color Change: The chemical reaction between citric acid and purple colored potassium permanganate solution is characterized by a change in color from purple to colorless.
The chemical reaction between sulfur dioxide gas and acidified potassium dichromate solution is characterized by a color change from orange to green.

(iii) Change of state of the substance: The combustion reaction of candle wax is characterized by a change of state from solid to liquid and gas (the wax being a solid, the water formed by the combustion of the wax is a liquid at room temperature while the carbon dioxide produced by the combustion of wax is a gas). Some chemical reactions can have several characteristics.

(iv) Change in temperature: The chemical reaction between quicklime water to form slaked lime is characterized by a change in temperature (which is an increase in temperature).
The chemical reaction between zinc granules and dilute sulfuric acid is also characterized by a change in temperature (which is a rise in temperature).

(v) Formation of precipitate: The chemical reaction between sulfuric acid and barium chloride solution is characterized by the formation of a white precipitate of barium sulfate.
Short technique for balancing a chemical equation:

Now let's try the short technique for balancing a chemical equation.

aKMnO4+ bHCl → cKCl + dMnCl2 + eH2O + fCl2

Now comparing the LHS and RHS, we obtain:

K: a = c

Mn: a = d

O: 4a = e

H: b = 2e

Cl: b = c + 2d + 2f

Let's take a = 2, then

c = d = a = 2

b = 2e = 8a = 16

So e = 8

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

f = 5

The required equation will be 2KMnO4+ 16HCl → 2KCl + 2MnCl2 + 8H2O + 5Cl2.

From the chemical reaction, we can obtain information on:

The names of various reagents and products

Reagent and product formulas

The number of moles of reactants and products relative to each other

Masses of reactants and products relative to each other

Volumes of reagents and gaseous products

Corrosion:
Many chemically active metals can be affected by oxygen, moisture, acids, etc. The process involving the change of a shiny layer that can sometimes turn reddish brown is known as corrosion, iron rusting is a common name used for this phenomenon. Oxidation does not adhere properly to the surface of the metal, causing the metal to weaken and break.

Rancidity: The process of changing the flavor and odor of food is known as rancidity. This happens due to oxidation, which leads to the deterioration of fats and fatty acids. This is the most common cause of rancidity.

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