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CBSE Notes
Class 10
Science
Chapter 1 Chemical Reactions and Equation

CBSE Notes Class 10 Science Chapter 1 - Chemical Reactions and Equation

Chemical reactions are a fundamental concept in chemistry that describes the transformation of substances in CBSE Class 10. The substances that undergo change are called reactants, and the new substances formed are known as products. This transformation can be expressed using chemical equations, where the symbols and formulas of the substances involved are written to represent a chemical change.

1.0Download CBSE Notes Class 10 Science Chapter 1: Chemical Reactions and Equation - Free PDF!!

Hey there! Looking to ace your Class 10 Science? These free PDF notes for Chapter 1, "Chemical Reactions and Equations," will give you a solid foundation for understanding the basics. Let's get started on mastering those chemical equations!

Class 10 Science Chapter 1 Revision Notes:

2.0What is a Chemical Reaction?

A chemical reaction is a process in which one or more substances (reactants) are transformed into different substances (products). This occurs when chemical bonds between atoms are broken and new bonds are formed. The change can be observed in various ways, such as color change, gas formation, precipitation, or temperature change. Here is an image representing balancing chemical equation-

example of a chemical reaction

Other Examples of Chemical Reactions:

  • Rusting of iron: 

4Fe + 3O2 → 2Fe2O3

  • Burning of magnesium in the air: 

2Mg + O2 → 2MgO

3.0Writing Chemical Equations

A chemical equation is the symbolic representation of a chemical reaction. It involves the chemical formulas of the reactants on the left side and the products on the right, separated by an arrow (→), which shows the direction of the reaction.

reactants and products in a chemical reaction

Example: The reaction of hydrogen with oxygen to form water can be written as:

                            2H2 + O2 → 2H2O 

In a chemical equation:

  • Reactants are written on the left side.
  • Products are written on the right side.
  • An arrow points from reactants to products, indicating the direction of the reaction.

4.0Balancing Chemical Equations

One of the most important skills in chemistry is balancing chemical equations. A balanced equation has the same number of atoms of each element on both sides. This is essential because matter cannot be created or destroyed (the Law of Conservation of Mass).

Steps to Balance a Chemical Equation:

  1. Write the unbalanced equation with the correct chemical formulas for all reactants and products.
  2. Count the number of atoms of each element on both sides.
  3. Adjust the coefficients (the numbers before the formulas) to balance the atoms.
  4. Ensure the coefficients are in the simplest whole number ratio.

Example: Balancing the equation for the formation of water:

                          H2 + O2 → H2O (unbalanced) 

Step 1: There are 2 hydrogen atoms on both sides but only 1 oxygen atom on the right side.

Step 2: Adjust the coefficient of water:

                         2H2 + O2 → 2H2O (balanced)

Now, both sides have 4 hydrogen atoms and 2 oxygen atoms.

5.0Types of Chemical Reactions

Chemical reactions can be classified into several types based on how the reactants transform into products. In Class 10, you’ll learn about five main types of reactions:

  1. Combination Reaction: In this type, two or more reactants combine to form a single product. Example: 2H2 + O2 → 2H2O
  2. Decomposition Reaction: A single compound breaks down into two or more simpler substances. Example: 2H2O2  → 2H2O + O2
  3. Displacement Reaction: In this reaction, one element replaces another in a compound. Example: Zn + CuSO4 → ZnSO4 + Cu
  4. Double Displacement Reaction: Two compounds exchange ions to form new compounds. Example: Na2SO4 + BaCl2 → BaSO4 + 2NaCl
  5. Oxidation-Reduction or Redox Reactions: In an oxidation-reduction (redox) reaction, one substance gains oxygen or loses electrons (oxidation), while another loses oxygen or gains electrons (reduction). Example: ZnO + C → Zn + CO
  • Zinc oxide (ZnO) is reduced to zinc (Zn) because it loses oxygen.
  • Carbon (C) is oxidised to carbon monoxide (CO) because it gains oxygen.

6.0Observations of Chemical Reactions

Certain observable changes indicate that a chemical reaction has taken place. These include:

Characteristics of chemical reaction

Observation

Description

Example

Change in Color

When the color of the reactants changes, it often indicates a reaction has occurred.

Copper turns black when heated in air due to the formation of copper oxide.

Evolution of Gas

Gas bubbles forming during a reaction can indicate a chemical change.

Zinc reacting with dilute hydrochloric acid evolves hydrogen gas.

Formation of Precipitate

A solid formed in a liquid reaction mixture indicates precipitation.

The reaction between sodium chloride and silver nitrate forms a white precipitate of silver chloride.

Change in Temperature

A reaction that releases or absorbs heat shows a temperature change.

Exothermic reactions like the reaction of calcium oxide with water release heat.

Corrosion: Corrosion is the gradual destruction of metals due to reactions with substances like moisture or acids. Rusting of iron, blackening of silver, and greening of copper are common examples.

Rancidity: Rancidity happens when fats and oils oxidize, changing their taste and smell. To prevent it, antioxidants are added, and foods are kept in airtight containers. Chips bags are flushed with nitrogen to slow oxidation.

7.0Solved Examples of Chemical Reactions and Equations

Q. Why does the colour of copper sulfate solution change when an iron nail is dipped in it?

Ans: The colour changes because iron displaces copper from copper sulfate solution, forming iron sulfate (greenish) and copper metal (brownish-red) is deposited on the nail.

Q. Identify the substances oxidized and reduced:

Ans:

i) 4Na(s) + O2(g) → 2Na2O(s)

  • Oxidized: Sodium (Na) – it gains oxygen.
  • Reduced: Oxygen (O₂) – it gains electrons.

ii) CuO(s) + H2(g) → Cu(s) + H2O(l)

  • Oxidized: Hydrogen (H₂) – it gains oxygen.
  • Reduced: Copper oxide (CuO) – it loses oxygen.

Q. Why should a magnesium ribbon be cleaned before burning in the air?

Ans: Magnesium ribbon is cleaned to remove the oxide layer that forms on its surface, allowing it to burn more easily.

Q. Write balanced chemical equations for given statements:

i) Barium chloride and Sodium sulfate reaction:

Sol.    BaCl2(aq) + Na2SO4(aq)   →   BaSO4(s) + 2NaCl(aq)

(Barium sulfate precipitate and sodium chloride solution form.)

ii) Sodium hydroxide and Hydrochloric acid reaction:

Sol.   NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

(Sodium chloride solution and water form.)

8.0Benefits of CBSE Notes Class 10 Science Chapter 1 Chemical Reactions and Equation

  • Building a Strong Foundation: This chapter lays a crucial foundation for understanding more complex chemical concepts in higher classes.
  • Improving Problem-Solving Skills: Practicing balancing equations and identifying reaction types enhances analytical and problem-solving abilities.
  • Preparing for Exams: Thorough understanding of this chapter is important for scoring well in CBSE board exams as it carries significant weightage.
  • Enhancing Retention: Studying notes and key points helps in quick revision and better retention of the concepts.
  • Connecting Theory to Practice: Relating chemical reactions to real-life examples makes learning more engaging and easier to grasp.

Chapter-wise CBSE Notes for Class 10 Science:

Class 10 Science Chapter 1 - Chemical Reactions and Equation Notes

Class 10 Science Chapter 2 - Acid Bases and Salts Notes

Class 10 Science Chapter 3 - Metals and Non-Metals Notes

Class 10 Science Chapter 4 - Carbon and Its Compounds Notes

Class 10 Science Chapter 5 - Life Processes Notes

Class 10 Science Chapter 6 - Control and Coordination Notes

Class 10 Science Chapter 7 - How Do Organisms Reproduce? Notes

Class 10 Science Chapter 8 - Heredity Notes

Class 10 Science Chapter 9 - Light Reflection and Refraction Notes

Class 10 Science Chapter 10 - Human Eye and Colorful World Notes

Class 10 Science Chapter 11 - Electricity Notes

Class 10 Science Chapter 12 - Magnetic Effects of Electric Current Notes

Class 10 Science Chapter 13 - Our Environment Notes



Chapter-wise NCERT Solutions for Class 10 Science:

Chapter 1: Chemical Reaction and Equations

Chapter 2: Acid Bases and Salts

Chapter 3: Metals and Non Metals

Chapter 4: Carbon and its Compounds

Chapter 5: Life Process

Chapter 6: Control and Coordination

Chapter 7: How Do Organisms Reproduce

Chapter 8: Heredity

Chapter 9: Light Reflection and Refraction

Chapter 10: Human Eye and Colourful World

Chapter 11: Electricity

Chapter 12: Magnetic Effects of Electric Current

Chapter 13: Our Environment

Frequently Asked Questions

Balancing chemical equations ensures the Law of Conservation of Mass is followed, meaning the same number of atoms of each element must be present on both sides of the equation.

In a decomposition reaction, a single compound breaks down into two or more simpler products.

Double displacement reactions are important in processes like precipitation, where two compounds exchange ions to form new compounds, often resulting in a precipitate. By learning these concepts, you are better prepared for both your board exams and higher-level chemistry studies.

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