Chemical Reactions and Equations
Class 10 Science Notes
1. Introduction to Changes
Q: What is change? What are its types?
Ans: A change is a transformation in the physical or chemical properties of a substance.
Classification of Changes:
1. Physical Change: A change in which the identity of the substance remains the same
and only its physical properties (such as shape, size, or state) are altered.
o Example: Melting of ice.
2. Chemical Change: A change that leads to the formation of a new substance with
different properties.
o Example: Rusting of iron, burning of paper.
2. Chemical Reactions and Equations
Q: What is a chemical reaction?
Ans: A chemical reaction is a process in which substances undergo a transformation,
resulting in the formation of new substances with different chemical properties.
Example: Burning of paper.
Q: What is a chemical equation?
Ans: It shows a chemical reaction using symbols and formulas to represent the reactants and
products involved.
Example: Hydrogen (H2) + Oxygen (O2) Water (H2O)
Q: Write the characteristics of a chemical reaction.
Ans: 1. Change in colour
2. Change in temperature
3. Change in state
4. Evolution of gas
, 5. Formation of a precipitate
Definition –
Precipitate: An insoluble solid which settles down after the completion of a chemical
reaction.
3. Balancing Chemical Equations
Q: What is the balancing of a chemical equation?
Ans: A balanced chemical equation is defined as an equation that consists of the same
number of atoms on both sides of the reaction.
Q: Why do we need to balance chemical equations?
Ans: We need to balance chemical equations because of the Law of Conservation of Mass,
which states that mass can neither be created nor be destroyed in a chemical reaction.
4. Energy in Reactions
Q: What are endothermic and exothermic reactions?
* Exothermic Reaction: The chemical reaction in which heat energy is released.
* Example: Respiration is an exothermic reaction.
Endothermic Reaction: The chemical reaction that absorbs heat energy.
o Example: Photosynthesis is an endothermic reaction.
5. Types of Chemical Reactions
There are four main types of chemical reactions:
I. Combination Reaction
A combination reaction is when two or more reactants join to form one new product.
Type 1: Combination of two elements to form a compound
Mg + O2 MgO
Class 10 Science Notes
1. Introduction to Changes
Q: What is change? What are its types?
Ans: A change is a transformation in the physical or chemical properties of a substance.
Classification of Changes:
1. Physical Change: A change in which the identity of the substance remains the same
and only its physical properties (such as shape, size, or state) are altered.
o Example: Melting of ice.
2. Chemical Change: A change that leads to the formation of a new substance with
different properties.
o Example: Rusting of iron, burning of paper.
2. Chemical Reactions and Equations
Q: What is a chemical reaction?
Ans: A chemical reaction is a process in which substances undergo a transformation,
resulting in the formation of new substances with different chemical properties.
Example: Burning of paper.
Q: What is a chemical equation?
Ans: It shows a chemical reaction using symbols and formulas to represent the reactants and
products involved.
Example: Hydrogen (H2) + Oxygen (O2) Water (H2O)
Q: Write the characteristics of a chemical reaction.
Ans: 1. Change in colour
2. Change in temperature
3. Change in state
4. Evolution of gas
, 5. Formation of a precipitate
Definition –
Precipitate: An insoluble solid which settles down after the completion of a chemical
reaction.
3. Balancing Chemical Equations
Q: What is the balancing of a chemical equation?
Ans: A balanced chemical equation is defined as an equation that consists of the same
number of atoms on both sides of the reaction.
Q: Why do we need to balance chemical equations?
Ans: We need to balance chemical equations because of the Law of Conservation of Mass,
which states that mass can neither be created nor be destroyed in a chemical reaction.
4. Energy in Reactions
Q: What are endothermic and exothermic reactions?
* Exothermic Reaction: The chemical reaction in which heat energy is released.
* Example: Respiration is an exothermic reaction.
Endothermic Reaction: The chemical reaction that absorbs heat energy.
o Example: Photosynthesis is an endothermic reaction.
5. Types of Chemical Reactions
There are four main types of chemical reactions:
I. Combination Reaction
A combination reaction is when two or more reactants join to form one new product.
Type 1: Combination of two elements to form a compound
Mg + O2 MgO
