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Hydrocarbons are an essential part of organic chemistry, which includes only hydrogen and carbon atoms in their molecular structure. They are a group of 14 hybrids. They occur naturally in nature in the form of certain emissions from vegetation.
- Hydrocarbons are also identified during the burning and combustion of fossil fuels.
- These compounds occur on earth in the form of crude oil, petroleum, and coal.
- They are colourless and hydrophobic in nature.
- The compound is the constituent of natural gas and petroleum.
- Hydrocarbons are combustible in nature and serve as the world's main energy source.
- Aliphatic and aromatic are two types of hydrocarbons.
- The molecular formula of these compounds is determined to be CxHy.
- It is also used in the form of fuel, which includes gasoline and jet fuel.
Read More: Hydrocarbons Important Questions
Key Terms: Hydrocarbons, Saturated Hydrocarbons, Alkanes, Alkenes, Saturated Hydrocarbon, Unsaturated Hydrocarbon, Substitution Reaction, Addition Reaction, Triple Bond
What are Hydrocarbons?
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Hydrocarbons can be defined as organic compounds consisting only of hydrogen and carbon atoms. These compounds are of different types and, thereby, have different natures.
- Hydrocarbons are usually colourless gases and are known for emitting faint odour.
- These have been classified under four major categories named as alkynes, alkanes, alkenes, and aromatic hydrocarbons.
- The composition of hydrogen and carbon atoms varies in each type.
Example of What are Hydrocarbons?Example: Coal consists of more atoms of carbon than hydrogen. They are very useful as a source of combustible fuel and serve a great deal in nature. Some forms of hydrocarbons, like methane, are considered as an important component of natural gas. |
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Types of Hydrocarbons
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Hydrocarbons can be classified under five special heads as stated below:
Saturated Hydrocarbons
Saturated hydrocarbons are those compounds where there is a single bond present between carbon atoms and are saturated with atoms of hydrogen. They are an important component of petroleum fuel.
- They form carbon bonds with hydrogen.
- They do not have double or triple bonds and undergo the process of hybridisation.
- CnH2n+2 is known as the formula for alkanes, which is the most common hydrocarbon.
- Saturated hydrocarbons have a similar molecular formula as hydrocarbons.
Unsaturated Hydrocarbons
Unsaturated hydrocarbons are hydrocarbons that consist of at least one double or triple bond between carbon atoms. Alkenes are organic compounds consisting of double bonds, whereas alkynes are triple-bonded.
- The situation is the opposite of saturated hydrocarbons.
- In this case, carbon atoms don't bond themselves with as many hydrogen atoms as possible.
- They are unsaturated when it comes to hydrogen atoms.
Aliphatic Hydrocarbons
Aliphatic hydrocarbons are generally chemical compounds. The term denotes the hydrocarbons formed as a result of the chemical degradation of fats. Its structure includes one or more hydrogen atoms, which are replaced with halogen.
- They are linked in chains in single, double or triple bonds without any rings.
- Propane, butane, methane, and ethane serve as good examples of aliphatic hydrocarbons.
Aromatic Hydrocarbons
Aromatic Hydrocarbons are also called arenes. They are distinguished by the benzene rings present in them. They give away different types of aroma. These hydrocarbons consist of only hydrogen and carbon atoms.
- They are used extensively in fields of medicine, fashion, and hygiene.
Read More: Rosenmund reduction reaction.
Properties of Hydrocarbons
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The properties of a hydrocarbon depends on its size to a great extent. The melting and boiling point varies in different types of hydrocarbons. Some important properties of hydrocarbons are as follows:
- Hydrocarbons emit a faint odour.
- Alkynes are highly reactive in the presence of a triple bond.
- The number of carbon atoms in a hydrocarbon determines its boiling point.
- They are nonpolar compounds, which means they are insoluble in water.
- Methane is present in gaseous form at room temperature.
- Alkanes are saturated hydrocarbons in contrast with alkenes and alkynes.
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| Electron Gain Enthalpy | Atomic Radius | Ions Definition |
Preparation of Hydrocarbons
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There are various methods used for the preparation of hydrocarbons which are as follows:
From Unsaturated Hydrocarbon
Hydrogenation is the process of creating alkane hydrocarbon in presence of nickel as the catalyst. The reaction is carried out at 200 degree celsius. In this dihydrogen gas is added to the required alkane, alkenes or alkynes.
- It is also known as Sabatier and Sanderson’s Reaction.
CH2=CH2 → (+Hz/Ni) CH3-CH3
From Alkyl Halides
The preparation of hydrocarbon with the use of alkyl halides can be created in two ways, which are as follows:
- In the first method, alkanes are formed by the reduction of alkyl halides with the use of zinc and hydrochloric acid.
- The reaction is expressed as:
CH3-Cl + H2 ------→ CH4 + HCl
- In the second method, alkyl halides are treated with sodium metal using dry ethereal.
- This reaction is also known as Wurtz Reaction.
CH3-Br + 2Na + Br-CH3 ------→ CH3-CH3 + 2NaBr
From Carboxylic Acids
There are two ways used for creation of alkanes by the use of carboxylic acids which are as follows:
Decarboxylation
Decarboxylation is a type of elimination reaction where carbon dioxide is eliminated from carboxylic acids. In this sodium salt of carboxylic acid is heated with mixture of sodium hydroxide and calcium oxide.
CH3COO-Na + NaOH ------→ CH4 + Na2CO3
Kolbe’s Electrolytic Method
In this process solution of sodium or potassium salt of carboxylic acid is heated to produce required alkane.
2CH3COO-Na + 2H2O ------→ CH3-CH3 + 2NaOH + 2CO2 + H2
Read More: Crystal Lattices and Unit Cells
Chemical Reactions of Hydrocarbons
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Hydrocarbons undergo three main chemical reactions which are as follows:
Substitution Reaction
Aromatic compounds are those hydrocarbons which are known to undergo Substitution reaction on a large scale. For example, benzene reacts with ethylene and gives ethylbenzene as the end product.
Addition Reaction
Addition reaction is restricted to only alkenes and alkynes. It also involves many reagents situated across pi bonds like chlorine, and water.
Combustion
When combustion of hydrocarbons takes place, flames are emitted consisting of heat and light energy. It is used as natural gas. It is the main source of electrical energy and is used in home heaters as well.
Read More: Decarboxylation Reaction
Uses of Hydrocarbons
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It can be observed that hydrocarbons has greater contribution in nature as well as our everyday needs which are as follows:
- Hydrocarbons are used as a combustible source of fuel, like methane.
- It is obtained after harvesting special plants to be used as a renewable source of energy for automobiles.
- The compound has the potential to replace diesel.
- Many industries devise hydrocarbons in the form of gasoline for their uses.
- They are collected and used as roofing compounds and wood preservatives.
- There is a special species of bees like the Brazilian stingless bees.
- The bees make use of hydrocarbons to emit scents and differentiate their family from others.
- They are commonly used in floor wax because of their insolubility in water.
Read More: Elementary Reactions
Important Topics for JEE MainAs per JEE Main 2024 Session 1, important subtopics included in the hydrocarbons are as follows:
Some memory based important questions asked in JEE Main 2024 Session 1 include:
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Things to Remember
- Hydrocarbons are organic compounds consisting of only hydrogen and carbon atoms.
- They are colourless compounds and depend upon their molecular composition.
- There are four major types of hydrocarbons, namely saturated, unsaturated, aliphatic, and aromatic hydrocarbons.
- Saturated hydrocarbons denote a single bond with the carbon atoms, whereas unsaturated hydrocarbons are completely opposite.
- Unsaturated hydrocarbons generally denote double or triple covalent bonds.
- The boiling point of a hydrocarbon fluctuates depending on the number of carbon atoms present in it.
- CNGs, fuels, and LPGs are hydrocarbons. Hydrocarbons can be present in the form of gas, liquid, or solid at room temperature.
- Alkenes and alkynes undergo an additional reaction, whereas hydrocarbons also go through combustion, giving out heat and light energy.
Read More: Rate Determining Step
Sample Questions
Ques. How is alkane prepared? (3 marks)
Ans. Alkanes are hydrocarbons, in the saturated form. They can be easily prepared from alkenes and alkynes. The process of hydrogenation is carried out here. Dihydrogen gas is passed over a metal surface and catalysts like nickel are present to speed up the reaction. Upon coming in contact with the alkenes and alkynes, they form into alkanes. Alkanes like ethane, butane, propane may even be formed with the help of alkyl halides.
Ques. What are the effects of hydrocarbons on nature? (4 marks)
Ans. We all know hydrocarbons are present everywhere on earth’s surface in the form of crude oil, petroleum, or coal. When these components are burned in the form of fuel, they emit harmful substances like carbon dioxide which has been known to be the biggest reason behind global warming.
- They are also released into the atmosphere by gas leaks in oceans, oil spills, or chemical explosions.
- It affects the quality of soil by eroding it and ultimately becomes toxic for human consumption.
- Agriculture as well as the health of humans is at a big risk due to such exposure of hydrocarbons in the environment.
Ques. Name some uses of hydrocarbons? (4 marks)
Ans. The uses of hydrocarbons are stated below:
- Hydrocarbons are excessively used as combustible fuels. For example LPGs and CNGs.
- Some insects like a unique species of bees make use of certain hydrocarbons as scents for distinguishing one’s family from others.
- Hydrocarbons are generally used as lubricating oil and grease.
- Some drugs also include hydrocarbons as their main element in their production.
- They are also used as wood preservatives and for making polythene.
Ques. What are unsaturated hydrocarbons? (3 marks)
Ans. Unsaturated hydrocarbons are those hydrocarbons which consist of double or even triple covalent bonds. These bonds are present between adjacent carbon atoms.
- The formation of an unsaturated hydrocarbon takes place in a straight line, as well as in the form of branches and aromatic compounds.
- They are very reactive in nature.
- Unsaturated hydrocarbons are insoluble in water, which is why they are called non-polar.
- Ethene and ethyne can be called as good examples of these types of hydrocarbons.
Ques. What are the properties of hydrocarbons? (3 marks)
Ans. Some of the crucial properties of hydrocarbons are as follows:
- Alkynes possess high boiling points in comparison with alkanes and alkenes.
- Hydrocarbons are colourless.
- They give away faint odour.
- Hydrocarbons can take the form of gases, solids, or liquids at room temperature.
- Hydrocarbons vary in size from each other.
- Hydrocarbons have low solubility in water.
Ques. Mention the reactions hydrocarbons undergo? (3 marks)
Ans. Hydrocarbons undergo three different kinds of reactions named as substitution reaction, addition reaction, and combustion. For example, in the case of addition reaction, it is constricted only to alkenes and alkynes. Many reagents like water, chlorine play an important role in this chemical process. The alkenes and alkynes end up undergoing polymerization.
Ques. What are some good examples of hydrocarbons? (3 marks)
Ans. Hydrocarbons are easily identifiable by their molecular structure. They are found in petroleum, coal, natural gas and crude oil. It is also used in fuel as a combustible source.
- All categories falling under aliphatic hydrocarbons are hydrocarbons like alkanes, alkenes, and alkynes.
- In addition to this, aromatic hydrocarbons like methane, ethane, propane also serve as good examples for hydrocarbons.
Ques. What is combustion? (3 marks)
Ans. Combustion can be called a chemical reaction between some substances which emit heat and light as their byproducts. These substances are usually a fuel and an oxidant like methane in reaction with oxygen. A more common example can be the reaction of hydrogen with oxygen in order to form water vapour. Combustion usually occurs in the form of flames.
Ques. Define aliphatic hydrocarbons? (3 marks)
Ans. Aliphatic hydrocarbons are organic compounds consisting of hydrogen and carbon atoms. These atoms are interlinked in a chain. The formation takes place with the help of single, double or triple bonds.
- These types of hydrocarbons are divided into three kinds: alkanes, alkenes, and alkynes.
- Alkanes consist of a single covalent bond.
- Methane is a good example for aliphatic hydrocarbons with one atom of carbon and 4 atoms of hydrogen.
Ques. What is the difference between alkene, alkane and alkyne? (4 marks)
Ans. The difference between alkene, alkane and alkyne are as follows:
| Alkene | Alkane | Alkyne |
|---|---|---|
| Alkene are type of hydrocarbon having double bond. | Alkane are type of hydrocarbon having single bond. | Alkyne are type of hydrocarbon having triple bond. |
| It is liquid in nature. | It is gaseous in nature. | It is solid in nature. |
| Alkene is little reactive. | Alkane is less reactive. | Alkyne is ost reactive. |
| It is used in rubber. | It is used in gasoline. | It is used in plastics. |
Ques. Explain the type of hydrocarbons? (4 marks)
Ans. There are four types of hydrocarbons which are as follows:
- Saturated hydrocarbons: Saturated hydrocarbons are those compounds where there is a single bond present between carbon atoms. They are an important component of petroleum fuel.
- Unsaturated hydrocarbons: Unsaturated hydrocarbons consisting of at least one double or triple bond between carbon atoms are known as unsaturated hydrocarbons. Alkenes are organic compounds consisting of double bonds, whereas alkynes are triple bonded.
- Aliphatic hydrocarbons: Aliphatic hydrocarbon are formed as a result of chemical degradation of fats. They are generally chemical compounds which includes one or more hydrogen atoms which are replaced with halogen.
- Aromatic hydrocarbons: They are distinguished because of the benzene rings present in them. They give away different types of aroma. These hydrocarbons consist of only hydrogen and carbon atoms.
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