Chemical Reactions & Eq. Important Questions Class 10 Science

When preparing for your Class 10 Science exams, one of the most important chapters is Chemical Reactions and Equations. This chapter lays the foundation for understanding the transformation of substances,  introducing students to the fascinating world of chemical transformations. The chapter is quite crucial for both board exams and competitive assessments. 

Understanding the basics of chemical reactions not only helps in scoring well but also lays a foundation for advanced studies in chemistry. This blog provides an expanded view of the chapter, offering insights, tips, and relatable examples to make your learning journey engaging and effective.

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PREMIUM EDUCART QUESTIONS

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(Most Important Questions of this Chapter from our 📕) 

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Chapter 1 Chemical Reactions and Equations Important Questions

When steam is passed through red hot iron, iron oxide and hydrogen gas is formed. The balanced equation for the reaction is shown below.

3Fe + 4H₂O  → Fe₃O₄ + 4H₂‍

(iron)   (water)      (iron oxide) (hydrogen)

1. Is heating iron to red hot a physical or a chemical change? Explain your answer. 

Ans. Heating iron to red hot is a physical change as no new substance is formed. 

Explanation

Iron changes color and softens when heated, but its chemical composition doesn't change. This is due to the absence of any new substance formation or chemical reaction.

The change is reversible and temporary. Once the iron cools, it returns to its original state.

A physical change affects the physical properties of a substance, such as shape, size, color, and condition, without altering its chemical structure.

2. What is true for the balanced chemical equation shown above?

1. Four atoms of water combine with iron to form four atoms of hydrogen. What is true for the balanced chemical equation shown above? 
2. Three atoms of iron combine with water to form four atoms of hydrogen. 
3. Four molecules of water combine with iron to form an atom of iron oxide. 
4. Three atoms of iron combine with water to form one molecule of iron oxide. 

Ans. ‍

(b)Three atoms of iron combine with water to form one molecule of iron oxide.  (B)

‍Explanation:

 Iron reacts with water to form iron oxide and hydrogen gas. This process is called rusting. The iron oxide forms a brown layer on the iron.

Cellular respiration is a chemical process by which cells convert glucose to energy. The equation given below shows the reaction for cellular respiration.  

C₆H₁₂O₆ + 6O₂→ 6CO₂ + 6H₂O + Energy

3. In the above reaction, which substance is oxidised?

Ans.  Glucose is oxidized. 

Explanation

‍Glucose is a carbohydrate, or sugar, that the body uses to provide energy to tissues and structures. However, the body can't use glucose in its raw form, so it must be broken down through a process called cellular respiration.

4. Carbon dioxide and water are the two new substances formed during cellular respiration. What are they known as?

1. Reactants
2. Mixtures
3. Catalysts
4. Products

Ans.

‍(d) Products‍

Explanation

‍Cellular respiration is a process that extracts energy from glucose and oxygen to produce carbon dioxide, water, and adenosine triphosphate (ATP). The reactants of cellular respiration are glucose and oxygen, while the products are carbon dioxide, water, and ATP. The overall chemical reaction for cellular respiration is glucose + oxygen → carbon dioxide + water.

A piece of magnesium ribbon is added to a flask containing dilute hydrochloric acid.  Hydrogen gas is formed which is collected in the measuring cylinder.  The amount of hydrogen formed with time is plotted on a graph.   The line on the graph indicates the rate of chemical reaction occurring in the flask.

5. At what time is the reaction rate the fastest in the flask?

1. At 1 minute 
2. At 3 minutes
3. At 4 minutes 
4. At 6 minutes

Ans.

‍(a) At 1 minute

‍Explanation: 

‍The reaction rate between magnesium and dilute hydrochloric acid is fastest at the beginning of the reaction, around 1 minute. This is because the amount of magnesium is at its highest at the start, which allows the reaction to proceed more rapidly. As the magnesium is consumed, the rate of the reaction gradually decreases.

6. The reaction is repeated with magnesium powder in place of magnesium ribbon under the same conditions. Will the reaction rate increase or decrease?

Explain your answer with reference to the volume of hydrogen formed in the flask at 2 minutes.

Ans.

‍The reaction rate will increase and therefore the volume of hydrogen formed at 2 minutes will be higher. 

‍Explanation

‍This is because magnesium powder has a larger surface area than magnesium ribbon, which allows more reactant particles to be exposed to the acid. This leads to more collisions between reactants and a faster reaction rate.

7. Which of these could increase the rate of reaction in the flask? Circle ‘Yes’ or ‘No’ for each row. 

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Ans.

‍Yes, Yes, Yes

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Explanation: 

All three factors will increase the rate of reaction when magnesium ribbon is added to hydrochloric acid (HCl):

1. Adding more acid to the flask: This increases the concentration of H⁺ ions in the solution, enhancing the chances of magnesium particles colliding with H⁺ ions, thereby increasing the reaction rate.
2. Heating the acid in the flask: Raising the temperature increases the kinetic energy of the particles, causing them to move faster and collide with greater force. This leads to a higher rate of reaction.
3. Using a higher concentration of acid: A higher concentration of HCl increases the number of H⁺ ions in the solution, which boosts the frequency of collisions between magnesium particles and H⁺ ions, accelerating the reaction.

8. Magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen gas.  Write a balanced chemical equation to show the reaction. 

Ans.

‍Mg + 2HCl → MgCl₂ + H₂

_‍Explanation:

‍Magnesium is more reactive than hydrogen and displaces it in the chloride molecule.

9. Which of these is an example of decomposition reaction?

1. Melting of glaciers 
2. Rusting of old bridges 
3. Rotting of fruits and vegetables 
4. Absorption of carbon dioxide by oceans

Ans.

‍(c) Rotting of fruits and vegetables. 

‍Explanation:

‍A decomposition reaction is a chemical reaction in which a single reactant breaks down into two or more products. In the case of rotting fruits and vegetables, the organic matter undergoes decomposition, breaking down into simpler substances.

10. Methane gas released from waste water treatment plants can be used as a source of fuel. Which chemical equation represents combustion of methane to produce heat energy?

A. CH₄ + CO₂→ 2O₂ + 2H₂O 

B. CH₄ + 2O₂→ CO₂ + 2H₂O 

C. 2O₂ + 2H₂O → CO₂ + CH₄ 

D. CO₂ + 2O₂→ CH₄ + 2H₂O 

Ans. 

‍(b) CH₄ + 2O₂→ CO₂ + 2H₂O

‍Explanation:

The reaction releases heat energy, making methane a valuable source of fuel. Therefore, the correct answer is (b) CH₄ + 2O₂→ CO₂ + 2H₂O

The Significance of Chemical Reactions

Chemical reactions are everywhere around us — from the rusting of iron and the digestion of food to the functioning of batteries and industrial processes. In this chapter, you will learn how substances interact to form new products, the laws governing these transformations, and how to represent them symbolically through equations.

Why is this Chapter Important?

Chemical reactions and equations are fundamental concepts in chemistry that demonstrate how matter interacts and transforms. Mastering this chapter enables students to:

• Identify different types of chemical reactions.
• Balance chemical equations.
• Predict products of reactions.
• Understand practical applications like corrosion, rancidity, and more.

Key Concepts to Focus On

Understanding Chemical Reactions:

• A chemical reaction occurs when one or more substances (reactants) change into new substances (products) with different properties.
• Example: When magnesium ribbon burns in the air, it forms magnesium oxide. 2Mg+O₂​→2MgO

Balancing Chemical Equations:

The law of conservation of mass states that the mass of reactants equals the mass of products in a reaction. This is the basis for balancing equations.

Tip: Always count the atoms of each element on both sides of the equation and use coefficients to balance them.

Types of Chemical Reactions:

• Combination Reactions: Two or more reactants combine to form a single product.

CaO+H₂​O→Ca(OH)_2​

• Decomposition Reactions: A single compound breaks down into two or more simpler substances.

2H₂​O_2​→2H₂​O+O₂​

• Displacement and Double Displacement Reactions: Involve the exchange of ions or atoms between compounds.

Zn+CuSO₄​→ZnSO₄​+Cu

• Oxidation and Reduction Reactions: Reactions involving gain or loss of oxygen or electrons.

Real-life Applications:

Corrosion: The gradual destruction of metals by chemical reactions with environmental elements.

Example: Rusting of iron.

Rancidity: The oxidation of fats and oils in food, leading to spoilage.

Study Tips for the Chapter

Understand the Core Principles: Grasp the concepts of reactants, products, and reaction conditions. Learn why and how reactions occur.

Practice Balancing Equations: Start with simple equations and gradually move to complex ones. Balancing equations strengthens your understanding of reaction stoichiometry.

Use Mnemonics for Reaction Types: Develop short phrases or keywords to remember reaction types and examples.

Make a Reaction Chart: Create a chart categorising reactions with their equations, characteristics, and examples. This will aid in quick revision.

Relate to Daily Life: Observe real-life chemical reactions, like cooking, cleaning, or using batteries, and connect them to the chapter's content.

Common Mistakes to Avoid

Ignoring State Symbols: Always include the physical states of reactants and products (solid (s), liquid (l), gas (g), or aqueous (aq)) in equations.

Skipping Steps in Balancing: Many students skip intermediate steps while balancing equations, leading to errors. Write each step clearly.

Confusing Reaction Types: Practice multiple examples of each reaction type to avoid confusion during exams.

How This Chapter Builds is Useful 

Understanding chemical reactions and equations is so crucial for advanced chemistry topics like stoichiometry, thermodynamics, and organic reactions. The skills acquired here are also essential for real-world applications in fields like chemical engineering, medicine, and environmental science.

The chapter Chemical Reactions and Equations is not just about memorising formulas and equations — it's about understanding the science of transformation. With consistent practice, a clear grasp of concepts, and an appreciation for their applications in everyday life, you can master this topic and excel in your Class 10 Science exams.

Start small, stay curious, and don't hesitate to seek help when needed. We hope that you practise the above Important Questions for Class 10 Science Chapter 1, Chemical Reactions and Equations and achieve your dream marks. Every step you take in learning chemistry is a step toward understanding the building blocks of the universe. Happy Learning! 

All the best!