Writing and Balancing Chemical Equations - UNSOLVED PRACTICE SET

Q7. What is a chemical equation? Write the skeleton equation and the balanced equation for the reaction between hydrogen and chlorine to form hydrogen chloride.

Q8. Why must chemical equations be balanced? Explain the principle behind balancing chemical equations.

Q9. Your younger brother is learning to write chemical equations. He writes: Mg + O₂ → MgO. Help him by explaining what is wrong with this equation and how to balance it correctly.

Q10. Balance the following chemical equations:

(a) Al + HCl → AlCl₃ + H₂

(b) Fe₂O₃ + CO → Fe + CO₂

Q11. Write balanced chemical equations for the following reactions, including state symbols:

(a) Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas.

(b) Calcium carbonate decomposes on heating to form calcium oxide and carbon dioxide.

Q12. What information does a balanced chemical equation provide? List any four pieces of information that can be obtained from a balanced chemical equation.

Q13. Explain the steps involved in writing and balancing a chemical equation. Illustrate with the example of the reaction between magnesium and oxygen to form magnesium oxide. Include state symbols and explain why balancing is essential according to the Law of Conservation of Mass.

Q14. A student is given the following unbalanced equations and is struggling to balance them:

(a) C₃H₈ + O₂ → CO₂ + H₂O

(b) Al₂(SO₄)₃ + NaOH → Al(OH)₃ + Na₂SO₄

(c) Pb(NO₃)₂ → PbO + NO₂ + O₂

Help the student by:

(i) Balancing each equation step by step.

(ii) Explaining the method used (inspection method or atom-by-atom method).

(iii) Verifying that each equation obeys the Law of Conservation of Mass.

(iv) Adding appropriate state symbols to each balanced equation.

Q15. "A balanced chemical equation is like a recipe that tells a chemist exactly what to mix and what to expect." Discuss this statement by explaining: (i) how a balanced equation gives information about reactants and products, (ii) how it helps in calculating the amounts of reactants needed, (iii) how state symbols help in understanding reaction conditions, and (iv) why an unbalanced equation is scientifically meaningless.

Q16. A chemistry teacher gives students a worksheet with the following reactions to balance:

(a) N₂ + H₂ → NH₃

(b) P₄ + O₂ → P₄O₁₀

(c) C₂H₆ + O₂ → CO₂ + H₂O

(d) KClO₃ → KCl + O₂

(e) BaCl₂ + Na₂SO₄ → BaSO₄ + NaCl

(i) Balance all five equations.

(ii) For reaction (c), calculate the total number of atoms on each side of the balanced equation.

(iii) For reaction (d), if 24.5 g of KClO₃ decomposes, calculate the mass of O₂ produced. (Molar masses: KClO₃ = 122.5 g/mol, O₂ = 32 g/mol)

(iv) For reaction (e), if 20.8 g of BaCl₂ reacts completely, calculate the mass of BaSO₄ precipitated. (Molar masses: BaCl₂ = 208 g/mol, BaSO₄ = 233 g/mol)

Q17. In a school laboratory, a student performs the following reactions and needs to write balanced equations:

Reaction 1: Burning of methane (CH₄) in a Bunsen burner

Reaction 2: Neutralization of sodium hydroxide with hydrochloric acid

Reaction 3: Reaction of copper oxide with hydrogen gas

Reaction 4: Electrolysis of water

(a) Write balanced chemical equations for all four reactions with state symbols.

(b) For Reaction 1, if 16 g of methane burns completely, calculate the mass of CO₂ produced. (Molar masses: CH₄ = 16 g/mol, CO₂ = 44 g/mol)

(c) For Reaction 4, if 9 g of water is electrolyzed, calculate the volume of hydrogen gas produced at STP. (1 mole of gas at STP = 22.4 L)

(d) Why is it important for the student to write balanced equations before performing quantitative experiments?

Q18. A chemical manufacturing plant produces calcium hydroxide (slaked lime) by reacting calcium oxide (quicklime) with water:

CaO + H₂O → Ca(OH)₂

(a) Balance the equation (if necessary) and add state symbols.

(b) If the plant uses 560 kg of calcium oxide daily, calculate the mass of calcium hydroxide produced. (Molar masses: CaO = 56 g/mol, Ca(OH)₂ = 74 g/mol)

(c) The plant also produces ammonia by the Haber process: N₂ + 3H₂ → 2NH₃. If 28 kg of nitrogen reacts with excess hydrogen, calculate the mass of ammonia produced. (Molar masses: N₂ = 28 g/mol, NH₃ = 17 g/mol)

(d) Why is it crucial for chemical engineers to work with balanced equations in industrial production? Give two reasons.

(e) If the plant wants to produce 100 tonnes of ammonia per day, how much nitrogen does it need? Show your calculation.