Hydrocarbons, Fractional Distillation, and Combustion Explained

Posted on Oct 11, 2024 in Chemistry

Hydrocarbons and Their Formulas

Empirical Formula: Simplest whole number ratio of each element in a compound (e.g., ethene = CH2).
Molecular Formula: Actual numbers of each element in a compound (e.g., ethene = C2H4).
General Formula: Represents the composition of any member of an entire class of compounds (e.g., alkenes = CnH2n).
Structural Formula: Shows the arrangement of atoms in the molecule of a compound (e.g., ethene = CH2CH2).
Displayed Formula: Shows the symbols for each atom in a compound, with straight lines representing covalent bonds.

Homologous Series and Functional Groups

Homologous Series: Series of compounds with the same general formula and similar properties.
Functional Group: A group of atoms responsible for the chemical reactions of a compound.

Isomerism and Reaction Types

Isomerism: Compounds with the same molecular formula but different arrangements of atoms.
Addition Reaction: Involves only one product.
Substitution Reaction: Involves two products.
Combustion Reaction: Involves the reaction of a fuel with oxygen.

Crude Oil and Fractional Distillation

Crude oil is a finite resource, a complex mixture of hydrocarbons containing molecules in which carbon atoms are in chains or rings. It’s an important source of fuels and feedstock for the petrochemical industry.

Fractional Distillation Process

  1. Crude oil is heated in a fractionating column.
  2. The oil evaporates and condenses at different temperatures.
  3. Hydrocarbons are separated into fractions based on their boiling points.
  4. Fractions are tapped off at different levels of the column.
  5. These fractions are processed into fuels and petrochemical feedstock.

Fractions and Their Uses

  • Refinery Gases: Domestic heating and cooking.
  • Gasoline/Petrol: Fuel for cars.
  • Kerosene: Fuel for aircraft.
  • Diesel: Fuel for some cars and trains.
  • Fuel Oil: Fuel for large ships and power stations.
  • Bitumen: Surface roads and roofs.

Properties of Hydrocarbons

  • Shorter molecules have lower boiling points and are less viscous.
  • Longer molecules have higher boiling points and are more viscous.
  • Colors darken with increasing molecular size.

Combustion and Its Effects

Fuel: A substance that releases heat energy when burned.

Complete Combustion: Produces carbon dioxide (CO2) and water (H2O).

Incomplete Combustion: Occurs with insufficient oxygen, producing soot (carbon), unburnt fuel, and carbon monoxide (CO). Carbon monoxide is poisonous, preventing red blood cells from carrying oxygen.

Acid Rain

Sulfur dioxide and nitrogen oxides react with rainwater to form H+ ions, creating acid rain. Acid rain corrodes rocks and buildings, damages ecosystems by altering soil and river pH, and corrodes limestone, impacting buildings and statues.

Cracking of Hydrocarbons

Cracking breaks down larger hydrocarbons into smaller, more useful molecules. This process involves heating hydrocarbons to vaporize them, then either passing them over a hot catalyst or mixing them with steam at high temperatures (600-700°C). Cracking produces alkanes and alkenes (CnH2n). Cracking helps meet the higher demand for smaller chained alkanes.