Organic ChemistryWorked Example
Writing and Balancing Cracking Equations
Part of Cracking (HT) — GCSE Chemistry
This worked example covers Writing and Balancing Cracking Equations within Cracking (HT) for GCSE Chemistry. Revise Cracking (HT) in Organic Chemistry for GCSE Chemistry with 24 exam-style questions and 0 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 6 of 14 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 6 of 14
Practice
24 questions
Recall
0 flashcards
🧮 Writing and Balancing Cracking Equations
Example 1: Crack C₁₂H₂₆ to form octane and an alkene
1. Write what we know: C₁₂H₂₆ → C₈H₁₈ + ?
2. Find missing carbons: 12 - 8 = 4 carbons
3. Find missing hydrogens: 26 - 18 = 8 hydrogens
4. Unknown product: C₄H₈ (butene — an alkene! CₙH₂ₙ check: 2×4=8 ✓)
Answer: C₁₂H₂₆ → C₈H₁₈ + C₄H₈
1. Write what we know: C₁₂H₂₆ → C₈H₁₈ + ?
2. Find missing carbons: 12 - 8 = 4 carbons
3. Find missing hydrogens: 26 - 18 = 8 hydrogens
4. Unknown product: C₄H₈ (butene — an alkene! CₙH₂ₙ check: 2×4=8 ✓)
Answer: C₁₂H₂₆ → C₈H₁₈ + C₄H₈
Example 2: Crack C₁₆H₃₄ to form ethene and an alkane
1. Write what we know: C₁₆H₃₄ → ?alkane + C₂H₄
2. Find remaining carbons: 16 - 2 = 14 carbons
3. Find remaining hydrogens: 34 - 4 = 30 hydrogens
4. Check if C₁₄H₃₀ is an alkane: 2(14)+2 = 30 ✓
Answer: C₁₆H₃₄ → C₁₄H₃₀ + C₂H₄
1. Write what we know: C₁₆H₃₄ → ?alkane + C₂H₄
2. Find remaining carbons: 16 - 2 = 14 carbons
3. Find remaining hydrogens: 34 - 4 = 30 hydrogens
4. Check if C₁₄H₃₀ is an alkane: 2(14)+2 = 30 ✓
Answer: C₁₆H₃₄ → C₁₄H₃₀ + C₂H₄
Key Rule: In cracking, you ALWAYS get at least one alkene. Alkenes have the general formula CₙH₂ₙ (two fewer hydrogens than the corresponding alkane CₙH₂ₙ₊₂).