CBSE Class 10 Science Notes & Important Question Chapter 1 Chemical Reactions and Equations

Here are some key points and notes for CBSE Class 10 Science Chapter 1, “Chemical Reactions and Equations”:

Chemical reactions are the processes in which one or more substances are transformed into new substances.
The reactants are the substances that are transformed during a chemical reaction, and the products are the new substances that are formed.
Chemical reactions can be represented using chemical equations, which show the reactants on the left-hand side and the products on the right-hand side, separated by an arrow.
Balancing chemical equations is important to ensure that the law of conservation of mass is upheld. This means that the total mass of the reactants must be equal to the total mass of the products.
Types of chemical reactions include:a. Combination reactions, in which two or more substances combine to form a new substance. b. Decomposition reactions, in which a single substance is broken down into two or more simpler substances. c. Displacement reactions, in which an element in a compound is displaced by another element. d. Double displacement reactions, in which two compounds exchange ions to form two new compounds.
Acids and bases are also involved in many chemical reactions. An acid is a substance that donates hydrogen ions (H+) in solution, while a base is a substance that accepts hydrogen ions.
The pH scale is a measure of the acidity or basicity of a solution. Solutions with a pH less than 7 are acidic, solutions with a pH greater than 7 are basic, and solutions with a pH of 7 are neutral.
Oxidation and reduction reactions involve the transfer of electrons between substances. An oxidizing agent is a substance that accepts electrons, while a reducing agent is a substance that donates electrons.
The law of conservation of energy states that energy cannot be created or destroyed, only transferred or converted from one form to another.
Endothermic reactions absorb energy, while exothermic reactions release energy.

These are some of the important points and notes for CBSE Class 10 Science Chapter 1, “Chemical Reactions and Equations”. Students should also refer to their textbooks and consult with their teachers for further information and clarification.

Here are some important questions for CBSE Class 10 Science Chapter 1, “Chemical Reactions and Equations”:

Define a chemical reaction. Give an example.
What is a reactant? What is a product? Give an example of each.
What is a chemical equation? Give an example.
Why is balancing a chemical equation important?
What is the law of conservation of mass?
Define a combination reaction. Give an example.
Define a decomposition reaction. Give an example.
Define a displacement reaction. Give an example.
Define a double displacement reaction. Give an example.
What is an acid? Give an example.
What is a base? Give an example.
What is the pH scale? How is it used to measure the acidity or basicity of a solution?
What are oxidation and reduction reactions?
What is an oxidizing agent? Give an example.
What is a reducing agent? Give an example.
What is an endothermic reaction? Give an example.
What is an exothermic reaction? Give an example.
State the law of conservation of energy.

Students should also refer to their textbooks and previous year question papers for more important questions and practice.

Here are the answers to the important questions for CBSE Class 10 Science Chapter 1, “Chemical Reactions and Equations”:

A chemical reaction is a process in which one or more substances are transformed into new substances. For example, the reaction of iron with oxygen to form rust is a chemical reaction.
A reactant is a substance that undergoes a change during a chemical reaction. For example, in the reaction of hydrogen with oxygen to form water, hydrogen and oxygen are the reactants. A product is a new substance that is formed as a result of a chemical reaction. In the same example, water is the product.
A chemical equation is a symbolic representation of a chemical reaction, with the reactants written on the left-hand side and the products on the right-hand side, separated by an arrow. For example: 2H2 + O2 → 2H2O
Balancing a chemical equation is important to ensure that the law of conservation of mass is upheld. This means that the total mass of the reactants must be equal to the total mass of the products, and no atoms are created or destroyed during the reaction.
The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction. The total mass of the reactants is equal to the total mass of the products.
A combination reaction is a type of chemical reaction in which two or more substances combine to form a new substance. For example: 2Mg + O2 → 2MgO
A decomposition reaction is a type of chemical reaction in which a single substance is broken down into two or more simpler substances. For example: 2H2O → 2H2 + O2
A displacement reaction is a type of chemical reaction in which an element in a compound is displaced by another element. For example: Zn + 2HCl → ZnCl2 + H2
A double displacement reaction is a type of chemical reaction in which two compounds exchange ions to form two new compounds. For example: AgNO3 + NaCl → AgCl + NaNO3
An acid is a substance that donates hydrogen ions (H+) in a solution. For example, hydrochloric acid (HCl) is an acid.
A base is a substance that accepts hydrogen ions (H+) in a solution. For example, sodium hydroxide (NaOH) is a base.
The pH scale is a measure of the acidity or basicity of a solution, ranging from 0 to 14. Solutions with a pH less than 7 are acidic, solutions with a pH greater than 7 are basic, and solutions with a pH of 7 are neutral. It is used to measure the concentration of hydrogen ions in a solution.
Oxidation and reduction reactions involve the transfer of electrons between substances. Oxidation is the loss of electrons, while reduction is the gain of electrons.
An oxidizing agent is a substance that accepts electrons during a chemical reaction. For example, oxygen (O2) acts as an oxidizing agent in many reactions.
A reducing agent is a substance that donates electrons during a chemical reaction. For example, hydrogen (H2) acts as a reducing agent in many reactions.
An endothermic reaction is a chemical reaction that absorbs energy from its surroundings. For example, the reaction between ammonium nitrate and water is endothermic.
An exothermic reaction is a chemical reaction that releases energy to its surroundings. For example, the combustion of gasoline is exothermic.

Here are some MCQs with answers for CBSE Class 10 Science Chapter 1, “Chemical Reactions and Equations”:

Which of the following is a chemical reaction?
a) Boiling water
b) Burning paper
c) Freezing water
d) Cutting an apple
Answer: b) Burning paper

What is a chemical equation?
a) A symbolic representation of a chemical reaction
b) A written description of a chemical reaction
c) A diagram of a chemical reaction
d) A measurement of a chemical reaction
Answer: a) A symbolic representation of a chemical reaction

What is the law of conservation of mass?
a) Mass is created during a chemical reaction
b) Mass is destroyed during a chemical reaction
c) Mass is neither created nor destroyed during a chemical reaction
d) Mass is only conserved during certain chemical reactions
Answer: c) Mass is neither created nor destroyed during a chemical reaction

What is a reactant?
a) A substance that is formed as a result of a chemical reaction
b) A substance that undergoes a change during a chemical reaction
c) A substance that causes a chemical reaction
d) A substance that is not involved in a chemical reaction
Answer: b) A substance that undergoes a change during a chemical reaction

What is a product?
a) A substance that is formed as a result of a chemical reaction
b) A substance that undergoes a change during a chemical reaction
c) A substance that causes a chemical reaction
d) A substance that is not involved in a chemical reaction
Answer: a) A substance that is formed as a result of a chemical reaction

What is the purpose of balancing a chemical equation?
a) To ensure that the law of conservation of mass is upheld
b) To ensure that the reaction occurs at the correct temperature
c) To ensure that the reaction occurs at the correct pressure
d) To ensure that the reaction occurs with the correct catalyst
Answer: a) To ensure that the law of conservation of mass is upheld

What is a combination reaction?
a) A reaction in which a single substance is broken down into two or more simpler substances
b) A reaction in which two or more substances combine to form a new substance
c) A reaction in which an element in a compound is displaced by another element
d) A reaction in which two compounds exchange ions to form two new compounds
Answer: b) A reaction in which two or more substances combine to form a new substance

What is an acid?
a) A substance that donates hydrogen ions (H+) in a solution
b) A substance that accepts hydrogen ions (H+) in a solution
c) A substance that causes a chemical reaction
d) A substance that is not involved in a chemical reaction
Answer: a) A substance that donates hydrogen ions (H+) in a solution

What is a base?
a) A substance that donates hydrogen ions (H+) in a solution
b) A substance that accepts hydrogen ions (H+) in a solution
c) A substance that causes a chemical reaction
d) A substance that is not involved in a chemical reaction
Answer: b) A substance that accepts hydrogen ions (H+) in a solution

What is an exothermic reaction?
a) A chemical reaction that absorbs energy from its surroundings
b) A chemical reaction that releases energy to its surroundings
c) A chemical reaction that occurs only at high temperatures
d) A chemical reaction that occurs only in the presence of a catalyst
Answer: b) A chemical reaction that releases energy to its surroundings