Why are alkanes the main constituents of petroleum gas, as opposed to other hydrocarbons?

Why are alkanes the main constituents of petroleum gas, as opposed to other hydrocarbons?

• A. Because they are the simplest molecules, making them the most stable
• B. Because they are heavier
• C. Because they have the highest boiling points
• D. Because they are more reactive

Answer: (A)

The situation hinges on the properties of small, saturated hydrocarbons. Alkanes with only a few carbon atoms—like propane and butane—are simple in structure, which keeps their boiling points low enough for them to be gases at room temperature while still allowing them to be compressed into liquids for storage as LPG. Their single bonds make them relatively stable and nonreactive, so they stay as a clean, predictable gas mixture until combustion. Heavier or more reactive hydrocarbons wouldn’t provide the same convenient gas behavior for storage and use, which is why the main components are these small, simple alkanes.

The situation hinges on the properties of small, saturated hydrocarbons. Alkanes with only a few carbon atoms—like propane and butane—are simple in structure, which keeps their boiling points low enough for them to be gases at room temperature while still allowing them to be compressed into liquids for storage as LPG. Their single bonds make them relatively stable and nonreactive, so they stay as a clean, predictable gas mixture until combustion. Heavier or more reactive hydrocarbons wouldn’t provide the same convenient gas behavior for storage and use, which is why the main components are these small, simple alkanes.