Overview
This lecture covers the physical properties of alkanes, how chain length affects these properties, and how to write and balance equations for their complete combustion.
Properties of Alkanes
- Alkanes are hydrocarbons containing only carbon and hydrogen with single (no double) bonds.
- As alkane chain length increases, boiling point rises.
- Alkanes with 1-4 carbons (methane to butane) are gases at room temperature; longer ones are liquids or solids.
- Shorter alkanes are more volatile (evaporate easily) due to low boiling points.
- Longer alkanes are more viscous (thicker and stickier).
- Shorter alkanes are more flammable, igniting more easily.
Combustion of Alkanes
- Alkanes are used as fuels because they release a lot of energy when burned in oxygen.
- Complete combustion occurs when there is enough oxygen, producing carbon dioxide and water.
- The reaction is exothermic (releases heat).
- During combustion, carbon and hydrogen are oxidized (combine with oxygen).
Writing and Balancing Combustion Equations
- To write the combustion equation: alkane + O₂ → CO₂ + H₂O.
- Balance carbon atoms first, then hydrogen, then oxygen.
- Example: For propane (C₃H₈):
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.
- Example: For nonane (C₉H₂₀):
C₉H₂₀ + 14O₂ → 9CO₂ + 10H₂O.
Key Terms & Definitions
- Alkane — A saturated hydrocarbon with only single carbon-carbon bonds.
- Boiling Point — The temperature at which a substance changes from liquid to gas.
- Volatile — Easily evaporates at normal temperatures.
- Viscous — Thick and sticky, resistant to flow.
- Flammable — Easily ignites and burns.
- Complete Combustion — Reaction with sufficient oxygen to produce only CO₂ and H₂O.
- Exothermic Reaction — A reaction that releases energy as heat.
Action Items / Next Steps
- Practice writing and balancing combustion equations for different alkanes.
- Review properties of alkanes with varying chain lengths.