Case Study:

During Diwali in India, fireworks are widely used for celebrations. Behind the colorful display lies a carefully balanced chemical reaction. A common mixture used in traditional fireworks contains potassium nitrate (KNO₃), sulfur (S), and carbon (C). When ignited, the simplified reaction can be written as:

KNO₃ + S + C -> K₂S + N₂ + CO₂

However, before manufacturing fireworks in licensed factories (such as those in Sivakasi, Tamil Nadu), chemists must balance this equation correctly to ensure complete combustion and controlled release of gases.

An unbalanced reaction can lead to incomplete combustion, excess smoke, or even dangerous explosions. For example, when balanced correctly, the reaction becomes:

2KNO₃ + S + 3C -> K₂S + N₂ + 3CO₂

Here, the correct ratio ensures proper formation of nitrogen gas and carbon dioxide, which create pressure that produces the bursting sound and visual effects.

Suppose a factory uses 202 g of KNO₃ (molar mass = 101 g/mol). According to the balanced equation, 2 moles of KNO₃ react with 3 moles of carbon. This means 202 g (2 moles) of KNO₃ require 36 g of carbon (3 × 12 g).

If excess carbon is added, more smoke forms. If less carbon is used, incomplete reaction reduces brightness.

Thus, balancing chemical equations is not just a classroom exercise — it ensures safety, efficiency, and environmental control in real-life applications.

Questions:

Section A - MCQs

1. Why is balancing the fireworks reaction important in manufacturing?
A. To increase cost of production
B. To ensure safety and controlled combustion
C. To change color of fireworks
D. To reduce the need for ignition

2. If 101 g of KNO₃ is used, how much carbon is required according to the balanced equation?
A. 12 g
B. 18 g
C. 36 g
D. 24 g

3. The bursting sound in fireworks is mainly due to:
A. Formation of solid potassium sulfide
B. Release of light energy only
C. Rapid formation and expansion of gases
D. Melting of sulfur

4. If excess carbon is added to the mixture, the most likely result is:
A. No reaction
B. Increased smoke formation
C. No gas production
D. Decrease in temperature

Section B - Short Answer Questions

1. Explain why an unbalanced chemical equation can lead to unsafe fireworks production.

2. Calculate the number of moles of KNO₃ in 202 g and explain how it helps in determining required carbon.

3. Identify the type of reaction occurring in fireworks and justify your answer.

Section C - Long Answer Question

1. A fireworks unit mistakenly uses 303 g of KNO₃.
(a) Calculate the amount of carbon required for complete reaction.
(b) What problems might arise if only 24 g of carbon is used instead?
(c) Suggest one environmental concern related to such reactions.

Answer Key:

Section A - MCQs

1. B
2. B
3. C
4. B

Section B - Short Answers

1. An unbalanced equation gives incorrect reactant ratios. This may cause incomplete combustion, excess pressure, or uncontrolled explosion, making production unsafe.

2. Moles = Mass / Molar mass
= 202 / 101 = 2 moles
Balanced equation shows 2 moles KNO₃ react with 3 moles carbon.
Hence, mole concept helps determine exact required quantity.

3. It is a combustion reaction because substances react rapidly with oxygen (from nitrate) producing heat, light, and gases.

Section C - Long Answer

1. (a) 303 g KNO₃
Moles = 303 / 101 = 3 moles

From balanced equation:
2 moles KNO₃ → 3 moles C
So 1 mole KNO₃ → 1.5 moles C
Therefore 3 moles KNO₃ → 4.5 moles C

Mass of carbon = 4.5 × 12 = 54 g

(b) If only 24 g carbon is used (2 moles), carbon is insufficient. Reaction will be incomplete, reducing brightness and causing improper gas formation.

(c) Environmental concern: Release of CO₂ and other gases contributes to air pollution and smog during festivals.