Why Cracking Always Produces At Least One Alkene
Part of Cracking (HT) — GCSE Chemistry
This how it works covers Why Cracking Always Produces At Least One Alkene 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 5 of 14 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 5 of 14
Practice
24 questions
Recall
0 flashcards
⚙️ Why Cracking Always Produces At Least One Alkene
Cracking is a thermal decomposition reaction — large hydrocarbon molecules are broken apart using heat energy. When a C-C bond breaks, the carbon atoms at the breaking point can form new double bonds with adjacent carbons, creating the C=C double bond that makes alkenes.
The atom conservation rule: The total number of carbon and hydrogen atoms on both sides of the cracking equation must be equal. This is a key check for any cracking calculation.
- If you crack a C₁₂H₂₆ alkane, all 12 carbons and 26 hydrogens must appear in the products
- Products include at least one alkane (CₙH₂ₙ₊₂) and at least one alkene (CₙH₂ₙ)
- The alkene always has 2 fewer hydrogens than the alkane of the same chain length — this is how you identify it
Why cracking doesn't produce alkenes through combustion: Cracking uses no oxygen — it breaks bonds through heat alone (thermal decomposition). It is very different from burning. Cracking produces new hydrocarbon products; combustion produces CO₂ and H₂O.