Chemical Reactions and Equations Class 10 Science Recap — Grandmaster Guide

• Chemical equation: a representation of a chemical reaction using symbols and formulas of reactants and products
• Law of conservation of mass: matter cannot be created or destroyed ∈ a chemical reaction, so the total mass of reactants = total mass of products
• Balanced chemical equation: a chemical equation ∈ which the number of atoms of each element is the same on both the reactant and product sides
• Combustion reaction: a reaction ∈ which a substance combines with oxygen to produce heat and light, e.g., 2CH₄ + 3O₂ → 2CO + 3H₂O
• Neutralization reaction: a reaction ∈ which an acid and a base combine to form a salt and water, e.g., HCl + NaOH → NaCl + H₂O
• Oxidation reaction: a reaction ∈ which a substance loses one or more electrons, e.g., 2Fe + O₂ → 2FeO
• Reduction reaction: a reaction ∈ which a substance gains one or more electrons, e.g., CuO + H₂ → Cu + H₂O
• Redox reaction: a reaction ∈ which both oxidation and reduction occur, e.g., 2Cu + O₂ → 2CuO

🪤 The 5 Mistakes That Cost Marks

• Not balancing chemical equations, e.g., Fe + O₂ → FeO (should be 4Fe + 3O₂ → 2Fe₂O₃)
• Not using the correct formulas for reactants and products, e.g., writing H₂O as HO
• Not indicating the physical states of reactants and products, e.g., writing 2H₂ + O₂ → 2H₂O (should be 2H₂(g) + O₂(g) → 2H₂O(l))
• Not using the correct coefficients ∈ balanced chemical equations, e.g., writing 2CH₄ + O₂ → 2CO + H₂O (should be 2CH₄ + 3O₂ → 2CO + 3H₂O)
• Not identifying the type of chemical reaction, e.g., writing a neutralization reaction as a combustion reaction

✏️ 3 Solved PYQs

• Question 1: What is the balanced chemical equation for the reaction between calcium carbonate and hydrochloric acid? Step 1: Write the unbalanced equation: CaCO₃ + HCl → CaCl₂ + H₂O + CO₂ Step 2: Balance the equation: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
• Question 2: What type of chemical reaction occurs when sodium hydroxide reacts with hydrochloric acid? Step 1: Write the balanced chemical equation: NaOH + HCl → NaCl + H₂O Step 2: Identify the reaction type: neutralization reaction
• Question 3: What is the oxidation number of iron ∈ Fe₂O₃? Step 1: Write the formula for iron(III) oxide: Fe₂O₃ Step 2: Determine the oxidation number of iron: +3

🧠 The One Thing Most Students Get Wrong

• Most students struggle with balancing chemical equations, especially when dealing with complex reactions involving multiple reactants and products
• To overcome this, practice balancing different types of chemical equations, including combustion, neutralization, and redox reactions
• Use the law of conservation of mass to ensure that the number of atoms of each element is the same on both the reactant and product sides

👁️ Ayush's Note

• When solving problems related to chemical reactions and equations, always start by writing the unbalanced equation
• Then, balance the equation by adding coefficients to the reactants and products
• Make sure to indicate the physical states of reactants and products using (s), (l), (g), or (aq)
• Finally, identify the type of chemical reaction and determine the oxidation numbers of the elements involved

🔁 Last 5 Minutes Box

• Quickly review the formulas for different types of chemical reactions, including combustion, neutralization, and redox reactions
• Practice balancing simple chemical equations, such as 2H₂ + O₂ → 2H₂O
• Make sure to use the correct coefficients and indicate the physical states of reactants and products
• Identify the type of chemical reaction and determine the oxidation numbers of the elements involved

📝 Practice MCQs

1. What is the balanced chemical equation for the reaction between zinc and hydrochloric acid?

A) Zn + HCl → ZnCl + H₂

B) Zn + 2HCl → ZnCl₂ + H₂

C) Zn + HCl → ZnCl₂ + H

D) Zn + 2HCl → ZnCl + 2H₂

Answer: B) Zn + 2HCl → ZnCl₂ + H₂

2. What type of chemical reaction occurs when methane burns ∈ oxygen?

A) Neutralization reaction

B) Combustion reaction

C) Redox reaction

D) Oxidation reaction

Answer: B) Combustion reaction

3. What is the oxidation number of oxygen ∈ H₂O?

A) +1

B) -2

C) +2

D) -1

Answer: B) -2

4. What is the balanced chemical equation for the reaction between sodium hydroxide and sulfuric acid?

A) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

B) NaOH + H₂SO₄ → NaHSO₄ + H₂O

C) 2NaOH + H₂SO₄ → Na₂SO₄ + H₂

D) NaOH + H₂SO₄ → NaHSO₄ + 2H₂O

Answer: A) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

5. What is the law of conservation of mass?

A) Matter cannot be created or destroyed ∈ a chemical reaction

B) Matter can be created or destroyed ∈ a chemical reaction

C) The total mass of reactants is less than the total mass of products

D) The total mass of reactants is greater than the total mass of products

Answer: A) Matter cannot be created or destroyed ∈ a chemical reaction

⚗️ Chemical Quick Reference (Verified via PubChem)

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📚 Academic References

Content verified against peer-reviewed research:

1. Bargaining in the Shadow of Big Data — Florida law review (2016) 🔓 — DOI ↗

🔓 = Open Access article

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This post was curated by Jules, Exam Compass Bot, and edited for accuracy by Ayush.

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