Physical Properties of Alkanes

Now suppose you are lighting your gas stove to cook something tasty. The fuel that you are using is probably a simple alkane, such as butane or propane. Alkanes are sometimes casually or roughly called paraffins. This is an entity flippantly found in most common commercial products derived from petroleum, like natural gas, gasoline, etc., and sometimes even in candles. Whether it is an automobile engine, a warming fire, or merely the reassuring light of a camping candle, all rely upon the special features of alkanes.

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This Story also Contains

1. Main Concept: Definitions and Explanations
2. Different Features of Alkanes:
3. State of Matter and Molecular Size:
4. The various important physical properties of alkanes are discussed below:
5. Applications and significance:
6. Some Solved Examples
7. Summary

Main Concept: Definitions and Explanations

Alkanes are saturated hydrocarbons; each carbon atom is joined to other carbon atoms with single covalent bonds and has the general formula: $\mathrm{CnH} 2 \mathrm{n}+2$ from which a homologous series of saturated hydrocarbons may be derived. The simplest alkane is methane, CH₄ , the next in the series being ethane$(\mathrm{CH} 4 \mathrm{CH} 4)$, followed by ethane $(\mathrm{C} 2 \mathrm{H} 6 \mathrm{C} 2 \mathrm{H} 6)$, propane $(\mathrm{C} 3 \mathrm{H} 8 \mathrm{C} 3 \mathrm{H} 8)$,etc. This chapter shall cover some of the fundamental properties of alkane liquid states, melting and boiling points solubility, and density, etc. Alkanes are relatively unreactive, due to the strong carbon-carbon and carbon-hydrogen bonds which also make them ideal for use as fuels and solvents respectively.

Different Features of Alkanes:

State of Matter and Molecular Size:

The nature of alkanes with normal temperature can give information on the molecular size. Lower alkanes a gas- methane /ethane/propane/butane- while with its five to sixteen carbon alkanes are liquids, and for those above it are solids. The difference is attributed to the increasing strength of the van der Walls forces with an increase in molecular size.
Alkanes normally have low melting and boiling points which are found to increase with increasing molecular weight. This can be further explained by the fact that the rate of increase in the size of alkanes is making more van der Wal forces operate on their increased surface areas. Also, it requires more energy for alkanes to undergo a state change. For instance, methane is said to have a boiling point of -161.5°C while that of octane is 125.7°C. Solubility and Density:
Being a nonpolar molecule, alkanes are not soluble in water, but they are soluble in the use of another nonpolar solvent like hexane. The density of oil is lesser than that of water; hence making the oil, which is also a mixture of different alkanes, float above the water.

The various important physical properties of alkanes are discussed below:

• State: Due to weak forces, the alkanes up to four carbon atoms, i.e., methane, ethane, propane, and butane are colorless, odorless gases but the next thirteen members are colorless, odorless liquids. Alkanes from C₁₈ onwards are colorless and odorless solids.
• Density: The density of alkanes increases very slowly with the rise of molecular mass until it becomes constant at about 0.8. Thus, all alkanes are lighter than water.
• Solubility: They are generally insoluble in polar solvents such as water but soluble in non-polar solvents like ether, carbon tetrachloride, benzene, etc. The solubility decreases with an increase in molecular mass.
• Boiling point: The boiling points of straight-chain or n-alkanes increase regularly with the increasing number of carbon atoms. Among the isomeric alkanes, the normal isomer has a higher boiling point than the branched-chain isomers. The greater the branching of the chain, the lower will be the boiling point.
• Melting point: The melting points of alkanes do not follow a very smooth gradation with the increase of molecular size. Alkanes with an even number of carbon atoms have a higher melting point than the next lower and next higher alkanes having an odd number of carbon atoms.

Applications and significance:

Real World Applications :
We will come to know about what alkanes are, what benefits the human race gets from them, and what losses also it has to bear so that we are able to enjoy the benefits. Methane forms a significant proportion of the natural gas that is used at home in providing heating services for buildings as well as cooking purposes. Propane is also another typical burning gas used in portable stoves and heating systems. The liquid alkanes, in this case octane, were the critical component of the gasoline, the most vital component in the powering of the internal combustion oils. Other important applications are in solid alkanes; the paraffin wax, which is employed in the making of candles and sealing agents.

Commercial and Industrial Significance:

On the other hand, as far as the academic work is concerned, the alkanes rank among the first examples of the organic compounds study and are utilized in creating a basis for ensuring the understanding of more complicated classes of the hydrocarbons. Apart from the fact that their properties are quite predictable, there is a feature of enables them to obtain the most informative description of molecular relations and phase transitions. Alkanes have found a lot of industrial use, mainly in the manufacture of fuels, lubricants, and petrochemicals. The understanding of their properties is very useful in the study of process refinements and the development of sources for material and energy use.

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Some Solved Examples

Example 1

Question: Which of the following exists in both gaseous as well as liquid state?

1) Ethane
2) Propane
3) Pentane
4) Butyl decane

Solution: Pentane exists in both gaseous and liquid states. Ethane and propane exist in a gaseous state, while butyl decane exists only in a liquid state.

Hence, the answer is option (3).

Example 2

Question: Arrange the following in decreasing order of their melting point: NeoPentane, n-Pentane, Isopentane.

1) $1>2>3$
2) $3>2>1$
3) $1>3>2$
4) $3>1>2$

Solution: For different isomers of an alkane, an alkane with a spherical shape molecule has the highest melting point due to the most compact packing in the solid state. Thus, the order is:

NeoPentane > n-Pentane > Isopentane.

Therefore, option (1) is correct.

Example 3

Question: Which one of the following has the minimum boiling point?

1) n-butane
2) 1-butyne
3) 1-butene
4) Isobutene

Solution: The boiling point follows the order:

1-butyne > 1-butene > n-butane > Isobutene.

Hence, the answer is option (4).

Summary

Their states of matter, melting and boiling points, solubility, and density are a result of molecular size and structure. The knowledge of properties is basically of practical significance in everyday life and industry. An understanding of the basic laws in chemistry is yielded from the knowledge gained through alkane research, and what they mean in practical outputs or generally in real life.