Chemical Reactions and Equations

Write a balanced chemical equation for the reaction between sodium hydroxide and hydrochloric acid. What type of reaction is this? [CBSE 2025]

What is observed when a solution of potassium iodide is added to silver nitrate solution? Write the balanced equation and name the type of reaction. [CBSE 2024]

Define the following with one example each: (a) Combination reaction (b) Decomposition reaction (c) Displacement reaction [CBSE 2023]

Why is respiration considered an exothermic reaction? Explain with equation. [CBSE 2022]

What happens when iron nails are placed in copper sulphate solution? Write the word equation and chemical equation. [CBSE 2021]

Mass of reactants = Mass of products Matter can neither be created nor destroyed in a chemical reaction

A + B → AB Two or more reactants combine to form a single product Example: C + O₂ → CO₂

AB → A + B Single reactant breaks into two or more products Example: 2H₂O → 2H₂ + O₂

A + BC → AC + B More reactive element displaces less reactive Example: Zn + CuSO₄ → ZnSO₄ + Cu

AB + CD → AD + CB Exchange of ions between reactants Example: AgNO₃ + NaCl → AgCl + NaNO₃

Oxidation: Loss of electrons / Gain of oxygen Reduction: Gain of electrons / Loss of oxygen

Steps to balance equations:

1. Write the unbalanced equation
2. Count atoms on both sides
3. Use coefficients (not subscripts)
4. Balance one element at a time
5. Check all atoms are balanced

Example: Fe + O₂ → Fe₂O₃ Balanced: 4Fe + 3O₂ → 2Fe₂O₃

Based on products formed:

• Combination: A + B → AB
• Decomposition: AB → A + B
• Displacement: A + BC → AC + B
• Double Displacement: AB + CD → AD + CB

Based on energy:

• Exothermic: Release heat
• Endothermic: Absorb heat