The chlorination of methane is a classic example of a radical chain reaction. It involves the substitution of one or more hydrogen atoms in methane by chlorine atoms. The reaction proceeds in three stages: initiation, propagation, and termination.

1. Initiation: This is the first step where the reaction starts. The chlorine molecule absorbs light energy and breaks down into two chlorine radicals. This process is called homolytic fission. The bond between the two chlorine atoms breaks, and each atom takes one electron from the bond, forming two chlorine radicals (Cl•). The dot represents an unpaired electron.

Cl2 + energy → 2Cl•

2. Propagation: This is the main part of the reaction where the actual substitution of hydrogen in methane by chlorine occurs. It happens in two steps:

a) A chlorine radical (Cl•) reacts with a methane molecule (CH4), taking away one hydrogen atom to form hydrochloric acid (HCl) and leaving behind a methyl radical (CH3•).

Cl• + CH4 → HCl + CH3•

b) The methyl radical (CH3•) then reacts with a chlorine molecule (Cl2), taking one chlorine atom to form chloromethane (CH3Cl) and leaving behind a chlorine radical (Cl•).

CH3• + Cl2 → CH3Cl + Cl•

The chlorine radical produced in the second step can then react with another methane molecule, and the cycle continues. This chain reaction can continue thousands of times.

3. Termination: This is the final step where the reaction stops. It occurs when two radicals react with each other to form a stable molecule. There are several possibilities, such as two chlorine radicals forming a chlorine molecule, a chlorine radical and a methyl radical forming chloromethane, or two methyl radicals forming ethane.

Cl• + Cl• → Cl2
Cl• + CH3• → CH3Cl
CH3• + CH3• → C2H6

In reality, the reaction doesn't stop at chloromethane. Further substitution can occur to form dichloromethane (CH2Cl2), trichloromethane (CHCl3), and tetrachloromethane (CCl4). However, the rate of further substitution decreases because C-Cl bonds are stronger than C-H bonds.

Question

The chlorination of methane is a classic example of a radical chain reaction. It involves the substitution of one or more hydrogen atoms in methane by chlorine atoms. The reaction proceeds in three stages: initiation, propagation, and termination.

1. Initiation: This is the first step where the reaction starts. The chlorine molecule absorbs light energy and breaks down into two chlorine radicals. This process is called homolytic fission. The bond between the two chlorine atoms breaks, and each atom takes one electron from the bond, forming two chlorine radicals (Cl•). The dot represents an unpaired electron.

Cl2 + energy → 2Cl•

2. Propagation: This is the main part of the reaction where the actual substitution of hydrogen in methane by chlorine occurs. It happens in two steps:

a) A chlorine radical (Cl•) reacts with a methane molecule (CH4), taking away one hydrogen atom to form hydrochloric acid (HCl) and leaving behind a methyl radical (CH3•).

Cl• + CH4 → HCl + CH3•

b) The methyl radical (CH3•) then reacts with a chlorine molecule (Cl2), taking one chlorine atom to form chloromethane (CH3Cl) and leaving behind a chlorine radical (Cl•).

CH3• + Cl2 → CH3Cl + Cl•

The chlorine radical produced in the second step can then react with another methane molecule, and the cycle continues. This chain reaction can continue thousands of times.

3. Termination: This is the final step where the reaction stops. It occurs when two radicals react with each other to form a stable molecule. There are several possibilities, such as two chlorine radicals forming a chlorine molecule, a chlorine radical and a methyl radical forming chloromethane, or two methyl radicals forming ethane.

Cl• + Cl• → Cl2
   Cl• + CH3• → CH3Cl
   CH3• + CH3• → C2H6

In reality, the reaction doesn't stop at chloromethane. Further substitution can occur to form dichloromethane (CH2Cl2), trichloromethane (CHCl3), and tetrachloromethane (CCl4). However, the rate of further substitution decreases because C-Cl bonds are stronger than C-H bonds.

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