1. 12.4 Properties of Alkanes
The different uses of alkane compounds result from their physical properties, including their solubility and density. The solid alkanes that make up waxy coatings on fruits and vegetables help retain moisture, inhibit mold, and enhance appearance.
Learning Goal Identify the properties of alkanes and write a balanced equation for combustion.

2. Uses of Alkanes
Alkanes with one to four carbons are gases at room temperature and are widely used as heating fuels.
methane, ethane, propane, butane
Butane has four carbons:
Alkanes with five to eight carbons are highly volatile liquids at room temperature, which makes them useful as fuels.
pentane, hexane, heptane, octane
Octane has eight carbons:

3. Uses of Alkanes
Alkanes with 9−17 carbons are liquids with higher boiling points and are found in motor oils, mineral oil, kerosene, diesel, and jet fuels.
Decane has 10 carbons:
Alkanes with 18 or more carbon atoms, known as paraffins, are waxy solids at room temperature.
Petroleum jelly, or Vaseline, is a semisolid mixture of hydrocarbons with more than 25 carbon atoms.

4. Melting and Boiling Points
Alkanes
have the lowest melting and boiling points of organic compounds.
contain only the nonpolar bonds of C — C and C — H.
exhibit only weak dispersion forces in the solid and liquid states.
Longer-chain alkanes have more dispersion forces.

5. Melting and Boiling Points
Branched alkanes
have lower boiling points than the straight-chain isomers.
tend to be more compact, reducing the points of contact between the molecules.
do not have linear shapes and cannot line up close to each other.

6. Melting and Boiling Points
Cycloalkanes
have higher boiling points than the straight-chain alkanes with the same number of carbon atoms.
have limited rotation of carbon bonds; they maintain their rigid structure and can be stacked closely together, which gives them many points of contact and attractions to each other.

7. Melting and Boiling Points
We can compare the boiling points of straight-chain alkanes, branched-chain alkanes, and cycloalkanes.

8. Combustion of Alkanes
The carbon–carbon single bonds in alkanes are difficult to break, which makes them the least reactive family of organic compounds. However, alkanes burn readily in oxygen to produce carbon dioxide, water, and energy. Alkane(g) + O2(g)  CO2(g) + H2O(g) + energy Δ

9. Combustion of Alkanes
Methane is the natural gas we use to cook our food and heat our homes. The equation for the combustion of methane (CH4) is written as follows: CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) + energy Propane is the gas used in portable heaters and gas barbecues. The equation for the combustion of propane (C3H8) is written as follows: CH4(g) + 5O2(g)  3CO2(g) + 4H2O(g) + energy Δ Δ

10. Solubility and Density of Alkanes
Alkanes are
nonpolar.
insoluble in water.
less dense than water.
flammable in air.
found in crude oil.
If there is an oil spill in the ocean, the alkanes in the crude oil do not mix with the water but float on top, forming a thin layer on the surface.

11. Oil Spills
In April 2010, an explosion on an oil-drilling rig in the Gulf of Mexico caused the largest oil spill in U.S. history, spilling at its maximum about 10 million liters per day.
Cleaning up an oil spill includes the following processes:
mechanical—a boom may be placed around the oil so that boats called skimmers can scoop it up and place it in tanks.
chemical—a substance that attracts oil is used to pick up the oil, which is then scraped off into recovery tanks.
microbiological—certain bacteria that ingest oil are used to break oil down into less harmful products.

12. Study Check
Butane (C4H10) is a fuel often used in lighters. Write a balanced equation for the complete combustion of butane.

13. Solution
Butane (C4H10) is a fuel often used in lighters. Write a balanced equation for the complete combustion of butane. 2C4H10(g) + 13O2(g)  8CO2(g) + 10H2O(g) Δ