CH4(g) + CI2(g) $\to$ CH2CI(s) + HCIg The major factor that influences the rate of the reaction above is

1. Analyze the Question

The reaction provided is: CH₄(g) + Cl₂(g) → CH₃Cl(g) + HCl(g) (Note: The chemical formula in your prompt contains a slight typo, but this is clearly a free-radical substitution reaction between methane and chlorine).

The question asks for the "major factor" that influences the rate of this specific reaction.

2. Explain the Concept

This reaction is a photochemical reaction. In organic chemistry, the reaction between alkanes (like methane) and halogens (like chlorine) does not occur spontaneously in the dark at room temperature.

The reaction proceeds via a free-radical mechanism consisting of three stages:

• Initiation: The chlorine molecule ($Cl_2$) absorbs energy from ultraviolet (UV) light, causing homolytic fission to produce two chlorine radicals ($Cl^\bullet$).
• Propagation: The radicals react with methane to form methyl radicals and eventually the product.
• Termination: Radicals combine to end the reaction.

Without the presence of light (specifically UV light), the chlorine molecule would not split into the reactive radicals needed to start the chain reaction.

3. Show the Solution

• Concentration: While concentration affects the rate of many reactions, it is not the initiating factor for this specific reaction.
• Catalyst: This reaction does not require a traditional catalyst; it requires a specific form of energy.
• Temperature: While heat can initiate radical reactions, light is the specific, primary requirement for this chlorination process to proceed at a significant rate under standard conditions.
• Light: The reaction is defined as a photochemical reaction. The energy from the light (photons) is what breaks the $Cl-Cl$ bond to initiate the process.

4. Identify the Answer

The major factor that influences the rate of this reaction is Light.

5. Exam Tip

Whenever you see a reaction involving an alkane and a halogen (like $Cl_2$ or $Br_2$) in your JAMB or WASSCE exams, look for UV light or hν (the symbol for a photon) in the options. These reactions are almost always photochemical!