Consider the following reaction equation: C$_{16}$H$_{34}$ → C$_5$H$_{12}$ + C$_{11}$H$_{22}$. The process represented by the equation is

Analyze the question

The equation shows one large hydrocarbon molecule, C₁₆H₃₄ (an alkane), breaking down into two smaller molecules: C₅H₁₂ (an alkane, pentane) and C₁₁H₂₂ (an alkene). We need to name this process.

Explain the concept

• Cracking: the breaking down of large, long-chain hydrocarbons into smaller, more useful ones (usually a shorter alkane plus an alkene). It is done with heat, or with heat and a catalyst. It is used in the petroleum industry to get more petrol (gasoline) from heavy fractions.
• Fermentation: the breakdown of sugars by enzymes (e.g. yeast) into ethanol and CO₂. It has nothing to do with hydrocarbons.
• Polymerization: the joining of many small molecules (monomers) into one large molecule, which is the opposite of what we see here.
• Reforming: the rearrangement of the structure of hydrocarbon molecules (e.g. straight chains into branched or cyclic ones) to improve petrol quality, without a big change in the number of carbon atoms.

Show the solution

1. Check the carbon balance: 16 = 5 + 11 ✔
2. Check the hydrogen balance: 34 = 12 + 22 ✔
3. One large molecule → two smaller molecules, one of which is unsaturated (C₁₁H₂₂ fits CₙH₂ₙ, the alkene formula). This is the signature of cracking.

Answer

The process is cracking, which is option A.

Tip

Think of "cracking" like cracking a long stick into shorter pieces: big molecule → smaller molecules (alkane + alkene). If you see small molecules joining into big ones, that's polymerization. If the products have the same number of carbons but a different shape, that's reforming.