Problem 3 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{C}_{3} \mathrm{H}_{\mathrm{s}}+\mathrm{Cl}_{2} \stackrel{\text { Light }}{\longrightarrow} \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{Cl}+\mathrm{HCl}\) is an example of (a) elimination (b) substitution (c) addition (d) rearrangement reaction

Step-by-Step Solution

Answer

It's a substitution reaction.

Step 1: Identify the reactants and products

Examine the given chemical equation: \( \mathrm{C}_{3}\mathrm{H}_{8} + \mathrm{Cl}_{2} \longrightarrow \mathrm{C}_{3}\mathrm{H}_{7}\mathrm{Cl} + \mathrm{HCl} \). Here, the original reactants are \( \mathrm{C}_{3}\mathrm{H}_{8} \) and \( \mathrm{Cl}_{2} \), while the products are \( \mathrm{C}_{3}\mathrm{H}_{7}\mathrm{Cl} \) and \( \mathrm{HCl} \).

Step 2: Determine the changes in the chemical structure

Notice that one hydrogen atom from \( \mathrm{C}_{3}\mathrm{H}_{8} \) is replaced by a chlorine atom, forming \( \mathrm{C}_{3}\mathrm{H}_{7}\mathrm{Cl} \). The displaced hydrogen combines with the remaining chlorine to form \( \mathrm{HCl} \).

Step 3: Classify the type of reaction

The replacement of an atom, specifically a hydrogen atom by a chlorine atom, signifies that this is a substitution reaction, where chlorine swaps positions with hydrogen.

Key Concepts

Chemical Reactions

Chemical reactions are processes in which substances, known as reactants, are transformed into different substances, known as products. This transformation involves breaking existing chemical bonds and forming new ones, resulting in a change of chemical properties. During a reaction, the atoms in the reactants rearrange to create products.

These reactions are integral to many natural processes and industrial applications. For example:

• Photosynthesis in plants, where carbon dioxide and water convert to glucose and oxygen under sunlight.
• Combustion reactions, such as burning wood to release energy.
• Synthesis reactions in industries to create new compounds.

Understanding the fundamentals of chemical reactions helps in predicting the behavior of matter under different conditions. It also aids in designing new materials with desirable properties by controlling reaction pathways.

Halogenation

Halogenation is a specific type of chemical reaction where a halogen atom is added to a compound. The halogens include elements like fluorine, chlorine, bromine, and iodine. A common example of halogenation involves adding chlorine to hydrocarbons, which are compounds made of hydrogen and carbon.

In the context of our exercise, halogenation occurs when chlorine ( C ) is added to propane ( C ). This results in the substitution of a hydrogen atom with a chlorine atom, creating an alkyl halide. Typically, this reaction requires a source of energy, such as light, to proceed.

• Light provides the energy needed to break the Cl-Cl bond, forming two chlorine radicals.
• These reactive radicals then replace hydrogen atoms in the hydrocarbon by breaking C-H bonds.
• The displaced hydrogen atoms pair with other chlorine radicals to form hydrogen chloride ( HCl).

This process is used in organic synthesis and has applications in producing solvents, refrigerants, and pharmaceuticals.

Organic Chemistry

Organic chemistry is the study of carbon-containing compounds and their structures, properties, and reactions. The versatility of carbon in forming stable bonds with many elements, including other carbon atoms, leads to the diversity of organic compounds.

At the heart of organic chemistry are hydrocarbons, such as alkanes, alkenes, and alkynes - compounds composed primarily of carbon and hydrogen. These hydrocarbons serve as the foundation for more complex molecules through various reactions.

In organic chemistry:

• Substitution reactions, like the one shown in our example, occur when one atom or group in a molecule is replaced by another.
• Halogenation, as a specific form of substitution, highlights the way elements like chlorine alter the structure of hydrocarbons.
• Understanding these principles is essential for creating new chemicals and materials used in everyday products.

The applications of organic chemistry range from fuels and plastics to the development of drugs and agricultural products, making it a vital field of study in both scientific and industrial contexts.