# Chemical Reactions and Equations Class 10 Notes – CBSE Science Chapter 1

## Chemical Reaction

• A chemical reaction is a process by which one chemical substance changes into another chemical substance. For instance: The rusting of iron, the curdling of milk, the digestion of food, breathing, etc.
• A chemical reaction results in a chemical change because a new material is created that has entirely different properties from the original substance.
• In a chemical reaction, atoms just rearrange themselves.
1. Reactants are chemicals that participate in a chemical reaction.
2. Products are the new compounds created as a result of a chemical process.

Example :

An illustration of a chemical reaction is the burning of magnesium in the air to produce magnesium oxide.
2Mg(s) + O2(g) → 2MgO(s)
The magnesium ribbon is cleaned with sandpaper before being burned in the air.
This is done to clean the magnesium ribbon’s surface of the basic magnesium carbonate protecting coating.

Reactant: Materials that participate in a chemical reaction are referred to as reactants.
Example: Mg and O2

Product: A newly created substance that results from a chemical reaction.
Example: MgO.

## Characteristics of Chemical Reactions

Any of the following observations can be used to determine a chemical reaction:

a) Evolution of a gas
b) Change in temperature
c) Formation of a precipitate
d) Change in color
e) Change of state

## Types of chemical reactions

Chemical reactions are divided into many groups while taking into account various parameters.
A few examples are:

● Combination
● Decomposition
● Single Displacement
● Double displacement
● Redox
● Endothermic
● Exothermic
● Precipitation
● Oxidation

## Chemical Reactions and Equations

Word equation

A chemical reaction is expressed using words rather than chemical formulas in a word equation. A chemical reaction, it aids in identifying the reactants and products.

A word equation, which is a condensed way of expressing a chemical reaction, is used to describe it. A word equation’s left side displays the names of the reactants. The names of the reactants are separated by a plus sign (+) if there are multiple reactants. A word equation’s right side displays the products. The names of the products are separated by a plus sign (+) if there are many products.

For example,
Sodium + Chlorine → Sodium chloride
According to the equation above, sodium and chlorine react to generate sodium chloride.

## Symbols of elements and their valencies

An element’s chemical code is represented by a symbol. Each element has a one- or two-letter atomic symbol, which is merely the name of the element in shortened form.
An element’s combining power is measured by its valency. It can be thought of as the number of electrons that an atom loses, gains, or shares with other atoms to form a molecule.

## Writing chemical equations

A chemical equation is the representation of a chemical reaction using symbols and the chemical formulas of the reactants and products.

• For solids, the symbol is “(s)”.
• For liquids, it is “(l)”.
• For gases, it is “(g)”.
• For aqueous solutions, it is “(aq)”.
• For gas produced in the reaction, it is represented by “(↑)”.
• For precipitate formed in the reaction, it is represented by “(↓)”.

### Balanced Chemical Equation

Each element has an equal amount of atoms on both sides of a balanced chemical equation.
Example: Zn + H2SO4 → ZnSO4 + H2
This equation is a balanced chemical equation since the amounts of zinc, hydrogen, and sulphate are equal on both sides.
Mass in a chemical process cannot be generated or destroyed, according to the Law of Conservation of Mass. The total mass of the elements present in the reactants and products must match for the law to hold true.

### Unbalanced Chemical Equation

aCaCO3 + bH3PO4 → cCa3(PO4)2 + dH2CO3

Set up a series of simultaneous equations, one for each element.

Ca: a=3c
C: a=d
O: 3a+4b=8c+3d
H: 3b=2d
P: b=2c
Let’s set c=1
Then a=3 and
d = a = 3
b = 2c = 2
So a=3; b=2; c=1; d=3

The balanced equation is
3CaCO3 + 2H3PO4 → Ca3(PO4)2 + 3H2CO3

## Types of chemical reactions

Chemical reactions are divided into many groups while taking into account various parameters.

### Combination Reaction:

The reaction in which two or more substances combine to form a new single substance.
Eg. C(s) + O2(g) →CO2(g)

### Decomposition reaction:

The reaction in which a single substance decomposes to give two or more substances.
A → B + C

Decomposition reactions can be of three types:

###### Thermal Decomposition:

When a decomposition reaction is carried out by heating.
Eg. CaCO3 (s) → CaO (s) + CO2 (g)
(calcium carbonate) (quick lime) (carbon dioxide)

###### Electrolytic Decomposition:

When decomposition is carried out by passing electricity.
e.g., 2H2O + electric current → 2H2 + O2

###### Photolytic Decomposition:

When decomposition is carried out in presence of sunlight.
e.g., 2AgCl (s) + sunlight → 2Ag (s) + Cl2 (g)

### Displacement Reaction:

The chemical reaction in which an element displaces another element from its solution.
Eg. Fe(s) + CuSO4(aq) → FeSO4 + Cu(s)

### Double Displacement Reaction:

The reaction in which two different atoms or groups of atoms are mutually exchanged.
Eg. Na2SO4 + BaCl2 → BaSO4(s) + 2NaCl

### Precipitation reaction:

The reaction which involves the formation of a precipitate (insoluble substance) is known as a precipitation reaction.
Eg. Pb(NO3)2(aq) + 2KI(aq) → 2KNO3(aq) + PbI2(s)

### Oxidation reaction:

The reaction in which a substance gains oxygen or loses hydrogen is called an oxidation reaction.
Eg. 2Cu(s) + O2(g)+ Heat → 2CuO(s)

### Reduction reaction:

The reaction in which a substance gains hydrogen or loses oxygen is called a reduction reaction.
Eg. C(s) + 2H2(g) → CH4(g)

### Redox reaction:

The reaction in which one reactant gets oxidized and the other reactant gets reduced is called an oxidation-reduction reaction or redox reaction. In this reaction, simultaneous oxidation and reduction reactions take place.
Eg. ZnO + C → Zn + CO
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2

### Exothermic Reactions:

Reaction in which heat is released along with the formation of products.
Eg. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + Heat

### Endothermic reactions:

The reactions which require energy in the form of heat, light, or electricity to break reactants are called endothermic reactions. Eg. 2Pb(NO3)2(s) + 2PbO(s) + 4NO2(g) + O2(g)

## How Oxidation Reactions Affect Us every day:

Corrosion: It is an unfavorable change that happens to metals when moisture, oxygen, acids, and bases attack them.
For example, Iron corrosion (rusting): Fe2O3. nH2O (Hydrated iron oxide)

Rancidity: Unwanted alteration that occurs in food products containing oil as a result of fatty acid oxidation.

Adding antioxidants to food ingredients, storing food in airtight containers, purging the air with nitrogen gas, and chilling are all rancidity prevention techniques.

## Conclusion

Every significant formula and idea presented in the chapter is covered in the Chemical Reactions and Equations Class 10 Notes. Quick revision notes for Chemical Reactions and Equations Class 10 Notes are available to you if you need an overview of a chapter. These notes will undoubtedly save you time on those hectic exam days.

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