Science is a subject that explains how the world around us is made of. Chemical reactions are used to explain the various processes that happen around us. From rust to decomposition, chemical reactions provides a deeper insight into how molecular interaction and changes that happens. In other words, the chapter 1 of CBSE class 10 Science explains how a substance changes form.
Learn more about chemical reactions and equations by exploring CBSE Notes for Class 10 Science Chapter 1. These CBSE notes are comprehensive and detailed, yet concise enough to glance through for exam preparations. Students can also download the CBSE Class 10 Science Chapter 1 Notes through the link below:
Download CBSE Science Notes for Class 10 Chapter 1
CBSE Class 10 Science Notes Chapter 1 –Â Chemical Reactions and Equations
Chemical Reaction
A chemical reaction is defined as a process by which 2 or more substance react with each other to form new substance.
Chemical Reaction take place when there is:
- Change in state
- Change in colour
- Evaluation of a gas
- Change in temperature
Chemical Equation
A Chemical Equation is a symbolic representation of a chemical reaction in the form of symbols and formulae where reactants are written on left hand side with a plus sign between them and product are written on right hand side with a plus sign between them.
For Eg: The burning of Magnesium in air is written as:
Magnesium + Oxygen → Magnesium oxide
(Reactants)Â Â Â Â Â Â Â Â Â Â Â Â Â (Product)
 Writing a Chemical Equations
The above word equations can be written in shorter way by using the chemical formulae as shown below:
Mg + O2 → MgO
Balanced Chemical Equation
A chemical equation is said to be balanced when the number of atom of each element is equal on both the side of the equation i.e
Number of atom of an element on reactant side = Number of atom of element on product side
How to Balance a Chemical Equation
The above equation is not balanced. Let’s try to balance it.
Step 1: First write the chemical equation.
Mg  + O2 → MgO
Step 2: List the number of atoms of different elements present in the equation as shown in the table below.
| Element | No. of atoms in reactants (LHS) | No. of atoms in products (RHS) |
| Mg | 1 | 1 |
| O | 2 | 1 |
Step 3: As we can see that the Mg atoms are balanced on both side but Oxygen atoms are different. So, to balance the equation atom;
| Atom of Oxygen | In reactants (LHS) | In products (RHS) |
| Initial | 2 | 1 |
| To balance | 2 | 1×2 |
Now, the equation becomes;
Mg + O2 → 2MgO
Step 4: As we see that, Mg atoms are still not balanced. To equalize the number of Mg atoms;
| Atom of Mg | In reactants (LHS) | In products (RHS) |
| Intial | 1 | 2 |
| To balance | 1×2 | 2 |
2Mg + O2 → 2MgO
Now, the equation is above chemical equation is completely balanced as the number of atoms in reactant and products are equal.
Type of Chemical Reactions
Here we have mentioned the different types of chemical reactions.
1) Combination Reaction: When two or more substance combine to form a new single substance then it is called as combination reaction.
Examples:
a) Formation of slaked lime from quick lime
CaO(s) + H2O(l) → Ca(OH)2 (aq) + Heat
(Quick Lime)Â Â Â Â Â Â Â Â Â Â Â (Slaked lime)
b) Burning of coal
C(s) + O2(g) → CO2(g)
c) Formation of water
2H2(g) + O2(g) → 2H2O(l)
2) Exothermic Reaction: Reaction in which heat is evolved is called exothermic reaction.
Examples:
a) Burning of natural gas
CH4(g) + 2O2(g) → CO2(g) + 2 H2O(g)
b) Respiration reaction
C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + Energy
3) Decomposition Reaction: When a substance decomposes to give two or more substance then it is known as decomposition reaction.
a) 2FeSO4(s)      Heat→ Fe2O3(s) + SO2(g) + SO3(g)
b) CaCO3(s)     Heat→ CaO(s) + CO2(g)
c) 2Pb(NO3)2(s)     Heat→ 2PbO(s) + 4NO2(g) + O2
4) Displacement Reaction: When an element displaces another element from its compound, a displacement reaction occurs.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Zn(s) + CuSO4(aq) →  ZnSO4(aq) + Cu(s)
Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s)
5) Double Displacement Reaction: When two different atoms or group of atoms are exchanged in a chemical reaction then it is called as a double displacement reaction.
Na2SO4(aq) + BaCl2(aq)  → BaSO4(s) + 2NaCl(aq)
6) Oxidation Reaction: When the gain of oxygen or loss of hydrogen atom take place then it is known as oxidation reaction.
2Cu + O2     Heat→ 2CuO
7) Reduction Reaction: When the loss of oxygen or gain of hydrogen atom take place then it is known as oxidation reaction.
CuO + H2     Heat→ Cu + H2O
8) Redox Reaction: Reaction in which oxidation and reduction take place simultaneously is known as Redox reaction.
ZnO + C → Zn + CO
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
Corrosion
When a metal is attacked by substances around it such as moisture, acid etc, it is said to corrode and this process is known as corrosion.
Example: Black coating on silver, Green coating on copper
Rancidity
The taste and odour of food material containing fat and oil changes when they are left exposed to air for long time. This is called Rancidity. It is caused due to oxidation of fat and oil present in food material. It can be prevented by adding antioxidants to the food material, storing food in air tight container, using flush bag with nitrogen gas.
After going through the notes, students can also check out the NCERT Solutions for class 10 Science Chapter 1 – Chemical reactions and equations and concepts for deeper learning. Keep learning and stay tuned for further updates on CBSE and other competitive exams. Download BYJU’S App and subscribe to YouTube channel to access interactive Maths and Science videos.