Cracking Crude Oil & Alkenes

Introduction to Crude Oil and Hydrocarbons

• Crude oil is a mixture of various hydrocarbons.

• Hydrocarbons can be separated based on the length of their carbon chains through fractional distillation.

• Shorter hydrocarbons are highly flammable and are more effective as fuels compared to longer chain hydrocarbons, which tend to be thick and viscous, making them less useful.

Cracking of Long Chain Hydrocarbons

Definition and Process

• Cracking is a method of breaking down long, less useful hydrocarbons into shorter, more flammable hydrocarbons.

• It is a type of thermal decomposition reaction, where heating causes the breakdown of molecules.

Methods of Cracking

1. Catalytic Cracking

   • Long chain hydrocarbons are vaporized and passed over hot powdered aluminum oxide (the catalyst), causing them to split into smaller hydrocarbons.

2. Steam Cracking

   • Hydrocarbon vapors are mixed with steam and heated to high temperatures to facilitate the breakdown into shorter chains.

Balanced Chemical Equations for Cracking

• Example: Cracking decane (C10H22) results in shorter hydrocarbons and alkenes.

• When decane is cracked, it can form an alkane (like heptane) and an alkene (like propene).

• To balance the equation:

  • Decane (C10H22) → Heptane (C7H16) + Propene (C3H6)

• The total number of carbons and hydrogens must be equal on both sides.

Example Calculation

• Cracking decane into another alkane and ethene (C2H4):

  • Remove carbons and hydrogens of ethene from decane:

    • Carbons: 10 (decane) - 2 (ethene) = 8 (alkane)

    • Hydrogens: 22 (decane) - 4 (ethene) = 18 (alkane)

• Resulting alkane formula is C8H18, leading to the equation:

  • C10H22 → C8H18 + C2H4

Homologous Series

• Alkanes and alkenes represent two separate homologous series:

  • Alkanes (saturated) contain only single bonds.

  • Alkenes (unsaturated) contain at least one double bond.

Features of Alkenes

1. Reactivity

   • Alkenes are more reactive than alkanes; they can decolorize bromine water from orange to colorless, indicating their presence.

2. Polymer Formation

   • Alkenes can react to form polymers because their double bonds can break, allowing connections to adjacent molecules.

Conclusion

• Understanding the concepts of cracking, the formation of alkenes, and their properties and behavior is crucial in chemistry, specifically related to hydrocarbons.