Hydrocarbon Families: Alkanes and Alkenes

Hydrocarbons are organized into families based on their chemical properties and functional groups. These families share similar characteristics and follow specific patterns.

Definition: A hydrocarbon family is a group of organic compounds with the same functional group and similar chemical properties.

Key features of hydrocarbon families include:

1. Shared general formula
2. Molecular formulae differing by CH₂ between neighboring compounds
3. Gradual variation in physical properties, such as boiling points
4. Similar chemical properties

The two main hydrocarbon families discussed are alkanes and alkenes.

Alkanes

Definition: Alkanes are saturated hydrocarbons with only single bonds between carbon atoms.

Characteristics of alkanes:

• General formula: CnH₂n+₂
• Saturated, meaning all carbon atoms are joined by single bonds
• Less reactive compared to alkenes

Alkenes

Definition: Alkenes are unsaturated hydrocarbons with at least one double bond between carbon atoms.

Characteristics of alkenes:

• More reactive than alkanes due to the presence of double bonds
• Can be tested using bromine water

Example: To test for alkenes, add bromine water to the compound. If the orange color of bromine water turns colorless, it indicates the presence of a C=C double bond in the molecule.

Highlight: The differences between alkanes and alkenes in hydrocarbons primarily lie in their bond structure and reactivity.

Molecular Structures and Fractional Distillation

This section explores the molecular structures of alkanes and the process of fractional distillation used to separate crude oil into useful fractions.

Molecular Structures of Alkanes

The first four alkanes in the series are:

1. Methane $CH₄$
2. Ethane $C₂H₆$
3. Propane $C₃H₈$
4. Butane $C₄H₁₀$

Each alkane has a unique structural formula and ball-and-stick model representation, illustrating the arrangement of carbon and hydrogen atoms in the molecule.

Fractional Distillation of Crude Oil

Definition: Fractional distillation is the process used to separate crude oil into simpler and more useful mixtures.

The fractional distillation process of crude oil explained:

1. Heated crude oil enters a tall fractionating column
2. The column is hot at the bottom and cooler towards the top
3. Vapors from the oil rise through the column
4. Vapors condense when they become cool enough
5. Liquids are led out of the column at different heights

Highlight: The separation of crude oil components is based on their boiling points, which are determined by the strength of intermolecular forces in each fraction.

Properties of Crude Oil Fractions

The properties of different crude oil fractions vary based on the size and structure of their hydrocarbon molecules. This section explores these properties and their implications for various applications.

Relationship Between Molecule Size and Properties

1. Small hydrocarbon molecules: Weak intermolecular forces Low boiling points Leave the distillation column as gases
2. Long hydrocarbon molecules: Stronger intermolecular forces High boiling points Leave the column as hot liquid bitumen

Fractions and Their Uses

The fractional distillation process yields several useful fractions, including:

1. Liquefied petroleum gases: Fuel for domestic heating and cooking
2. Petrol: Fuel for cars
3. Kerosene: Fuel for aircraft
4. Diesel: Fuel for some cars and trains
5. Heavy fuel oil: Fuel for ships and power stations
6. Bitumen: Used for roads and roofs

Properties of Fractions

The properties of different fractions vary based on:

1. Number of hydrogen and carbon atoms in their molecules
2. Boiling points
3. Viscosity
4. Ease of ignition

Highlight: There is a clear trend in properties from small molecules to large molecules:

• Small molecules: Low boiling point, very volatile, flow easily, ignite easily
• Large molecules: High boiling point, not very volatile, do not flow easily, do not ignite easily

Detailed Properties of Extreme Fractions

This section focuses on the properties of the lightest and heaviest fractions obtained from crude oil distillation, highlighting the significant differences between them.

Gases Fraction

The gases fraction contains hydrocarbons with one to four carbon atoms. These have the following properties:

1. Boiling points below room temperature
2. Highly flammable
3. Low viscosity

Example: Methane $CH₄$, the simplest alkane, is a primary component of natural gas and has a boiling point of -161.5°C at atmospheric pressure.

Bitumen Fraction

The bitumen fraction contains hydrocarbons with more than 35 carbon atoms. These have the following properties:

1. Boiling points well above room temperature
2. Very difficult to ignite
3. High viscosity

Highlight: The stark contrast in properties between the gases fraction and the bitumen fraction demonstrates the wide range of applications for different crude oil components.

Vocabulary: Viscosity refers to a fluid's resistance to flow. Low viscosity fluids flow easily, while high viscosity fluids are thick and flow slowly.

These extreme fractions illustrate the versatility of crude oil as a finite resource and its applications in various industries, from fuel production to road construction.

Crude Oil and Hydrocarbons: Composition and Applications

Crude oil is a finite resource found in the Earth's crust, primarily composed of hydrocarbons. It serves as a crucial source of various fuels and petrochemicals, playing a significant role in modern industry and daily life.

Definition: Hydrocarbons are compounds that contain only hydrogen and carbon atoms.

Crude oil as a finite resource and its applications are extensive, including:

1. Fuels: Petrol, diesel, kerosene, heavy fuel oil, and liquefied petroleum gases
2. Feedstock for the petrochemical industry

Vocabulary: Feedstock refers to raw materials used to provide reactants for industrial reactions.

Other useful substances derived from crude oil compounds include:

• Solvents: Liquids used to dissolve solutes and form solutions
• Lubricants: Substances that reduce friction between surfaces
• Detergents: Mixtures of chemicals with cleaning properties when dissolved in water

Highlight: Crude oil is not only a source of fuel but also a vital raw material for producing various everyday products.