Chemistry Notes - Fuels and Earth Science

Hydrocarbons are compounds composed exclusively of carbon (C) and hydrogen (H) atoms.

Crude Oil Characteristics:
- A complex mixture of hydrocarbons.
- Contains molecules in which carbon atoms are arranged in chains or rings. (Note: The names, formulas, and structures of specific ring molecules are not required for this study.)
- An important source of useful substances, including fuels and feedstock for the petrochemical industry.
- A finite resource, meaning it is limited and not renewable.

Fractional Distillation Process:
- Crude oil is a mixture of various hydrocarbons, and each has a unique boiling point.
- Longer chain hydrocarbons possess higher boiling points.
- The crude oil is heated in a fractionating column:
- The oil evaporates and condenses at different temperatures.
- Heated crude oil is piped into the bottom of the fractionating column.
- Vaporized oil rises up the column, and different fractions condense at various levels where they are tapped off.
- Resulting fractions can be processed further to produce fuels and petrochemical feedstocks.

Characteristics of Hydrocarbons in Different Fractions:
- Differ in the number of carbon (C) and hydrogen (H) atoms in their molecules.
- Vary in boiling points, ease of ignition, and viscosity.
Properties Depend on Molecular Size:
- Short-chain hydrocarbons are less viscous (more runny) and have lower boiling points.
- Shorter hydrocarbons also ignite easier, making them more flammable.

A homologous series consists of compounds that:
- Share the same general formula.
- Differ from each other by a \text{CH}_2 unit in their molecular formulas.
- Exhibit gradual variations in physical properties, such as boiling points.
- Show similar chemical properties.

Complete Combustion Reaction:
- Produces carbon dioxide (CO₂) and water (H₂O).
- Releases energy in an exothermic reaction.

Caused by insufficient oxygen leading to:
- Partial Combustion: Some fuel does not burn completely.
- Products of Incomplete Combustion:
- Solid particles of soot (carbon).
- Carbon monoxide (CO), produced when there is not enough oxygen to form CO₂.

Carbon Monoxide as a Toxic Gas:
- A colorless and odorless gas.
- Prevents red blood cells from transporting oxygen throughout the body, leading to potential death upon inhalation.

Health Risks of Carbon Monoxide:
Soot Production Consequences:
- Causes global dimming, reflecting sunlight away from the Earth's surface.

Effects of Acid Rain:
- Damages buildings and statues, particularly those made from limestone.
- Reduces growth or kills trees and crops.
- Lowers water pH in lakes, which can kill aquatic life.

Formation of Nitrogen Oxides:
- Nitrogen and oxygen from the air can react at high temperatures in engines.
- This reaction produces nitrogen monoxide (NO), which further reacts with oxygen forming nitrogen dioxide (NO₂).
- Both nitrogen monoxide and nitrogen dioxide are classified as pollutants.

Advantages of Hydrogen:
- Derived from sources such as water; petrol is derived from finite crude oil.
- The combustion of hydrogen only produces water, contributing no CO₂ emissions, which is beneficial for combating global warming.
Disadvantages of Hydrogen:
- Higher costs associated with production and usage.
- Transport and storage of hydrogen can be challenging and unsafe due to its explosive nature.

Petrol, Kerosene, and Diesel Oil:
- All are non-renewable fossil fuels obtained from crude oil.
Methane:
- Considered a non-renewable fossil fuel found in natural gas.

Cracking Definition:
- The process of breaking down larger saturated hydrocarbons (alkanes) into smaller, more useful hydrocarbons, some of which become unsaturated (alkenes).
Cracking Procedure:
- Involves heating hydrocarbons to vaporize them.
- The vapors are either:
- Passed over a hot catalyst.
- Mixed with steam and heated to very high temperatures for thermal decomposition reactions.
Products of Cracking:
- Produces alkanes and alkenes.
- Alkenes:
- Have a general formula of $CnH{2n}$ .
- The first two alkenes are ethene (C₂H₄) and propene (C₃H₆) and are referred to as unsaturated due to the presence of a double bond.

Hydrocarbons: Compounds of carbon ( $C$ ) and hydrogen ( $H$ ) only.
Crude Oil: A finite complex mixture of hydrocarbons used for fuels and petrochemical feedstock.

Process: Crude oil is heated in a fractionating column. Hydrocarbons separate by boiling point; vapors rise and condense at specific levels.
Chain Length Correlation:
- Short-chain: Lower boiling point, lower viscosity (runnier), and higher flammability.
- Long-chain: Higher boiling point and higher viscosity.
Fractions: Gases (heating), Petrol (cars), Kerosene (aircraft), Diesel (trains), Fuel oil (ships), Bitumen (roads).

Complete Combustion: Produces $\text{CO}2$ and $\text{H}2\text{O}$ .
Incomplete Combustion: Occurs with limited oxygen; produces carbon monoxide ( $\text{CO}$ ) and soot (carbon particles).
Hazards:
- $\text{CO}$ : Toxic, colorless, and odorless; prevents oxygen transport in blood.
- Soot: Causes respiratory issues and global dimming.

Sulfur Dioxide ( $\text{SO}_2$ ): Formed from sulfur impurities; causes acid rain which damages buildings and ecosystems.
Nitrogen Oxides ( $\text{NO}_x$ ): Formed in high-temperature engines when atmospheric nitrogen and oxygen react.

Pros: Non-finite (from water), only produces $\text{H}2\text{O}$ (no $\text{CO}2$ ).
Cons: Expensive, difficult to store, and explosive risk.

Definition: Breaking long alkanes into smaller alkanes and alkenes using heat and a catalyst.
Alkenes: General formula $CnH{2n}$ ; contains a double bond (unsaturated). Examples: ethene ( $C2H4$ ) and propene ( $C3H6$ ).