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Summary of the Properties and Uses of Hydrocarbons

Name	Molecular Formula	Molecular Mass	Melting Point (^oC)	Boiling Point (^oC)	State (25^oC, 101.3kPa)	Density (liquid g cm^-3, 20^oC)	Flashpoint (^oC)	Enthalpy of Combustion (kJ mol^-1)	Uses
methane	CH₄	16	-182	-162	gas			-889	major component of natural gas (fuel)

ethane	C₂H₆	30	-183	-88.6	gas			<-1557	component of natural gas (fuel)

propane	C₃H₈	44	-188	-42.1	gas			-2217	component of liquefied petroleum gas (LPG), bottled gas (fuel)

butane	C₄H₁₀	58	-138	-0.5	gas			-2874	component of liquefied petroleum gas (LPG), cigarette lighters (fuel)

pentane	C₅H₁₂	72	-130	36.1	liquid	0.626	-49	-3536	component of petrol (fuel)

hexane	C₆H₁₄	86	-95.3	68.7	liquid	0.659	-22	-4190	component of petrol (fuel)

heptane	C₇H₁₆	100	-90.6	98.4	liquid		-4	-4847	component of petrol (fuel)

octane	C₈H₁₈	114	-56.8	126	liquid			-5506	major component of petrol (fuel)

nonane	C₉H₂₀	128							component of petrol (fuel)

decane	C₁₀H₂₂	142	-30	174	liquid	0.730			component of petrol (fuel)

hexadecane	C₁₆H₃₄	226	18.5	288	liquid	0.775			component of diesel fuel & heating oil

eicosane	C₂₀H₄₂	282	36	343	solid

Trends

Alkanes are colourless
methane to butane are colourless gases
(propane and butane are easily condensed under pressure & are commonly sold as liquids)
alkanes containing 5 carbons up to about 19 are colourless liquids
(petrol & kerosene are mixtures of liquid alkanes, dye is added to the fluids for safety reasons)
alkanes with more than about 20 carbon atoms are colourless, waxy solids
(paraffin wax is a mixture of solid alkanes)
Alkanes are less dense than water (alkanes will float on top of water)
density increases with increasing molecular mass
Simple alkanes have low melting and boiling points.
Alkanes are non-polar so only weak intermolecular forces act between the alkane molecules
(Van der Waal's Forces/London Forces/Dispersion Forces/Weak Intermolecular Forces)
Melting and Boiling Points increase as the molecular mass increases
Alkanes are insoluble in polar solvents like water
Alkanes are relatively unreactive
(they will combust: commonly used as fuels since large amounts of energy are released, the longer the chain, the more bonds are broken, the greater the energy released)
(will undergo halogenation by substitution reaction in the presence of ultra-violet light)
Alkanes with *flashpoints below room temperature (the components of petrol for example) should be stored in strong metal containers with narrow mouths & tightly sealed lids to prevent the vapour from escaping & to prevent a naked flame or spark from igniting the vapour/air mixture.

*Flashpoint: the minimum temperature at which the vapour pressure of a liquid is high enough for an explosive mixture to be formed with air. Safety precautions for handling & storing fuels are determined by the flashpoint.