Alkane Action: Substitution with Chlorine
Watch methane swap hydrogen for chlorine
What this lesson covers
Why it matters
Mix methane and chlorine in the dark and nothing happens. Shine a light, and the mixture reacts violently to form new compounds.
The idea in plain words
Analyze the equation: CH₄ + Cl₂ → CH₃Cl + HCl. Note the 1:1 swap of H for Cl.
Predict first
What happens when methane reacts with chlorine in sunlight?
Alkanes undergo substitution, where a hydrogen atom is swapped for a halogen atom under UV light.
- Chlorine adds to methane to form CH₂Cl₂
- A hydrogen atom is replaced by a chlorine atom — correct
- No reaction occurs without a catalyst
What you do
Expose the methane-chlorine mixture to sunlight. The methane and chlorine react and colourless hydrogen chloride (HCl) gas is given off. (HCl shows up as dense white fumes only when it meets ammonia vapour.)
Check yourself
Which condition is essential for this substitution reaction?
The reaction is photochemical; it requires light energy to break the Cl-Cl bond.
How do you test for the gaseous byproduct formed?
The byproduct is HCl gas, which reacts with ammonia vapor to form white ammonium chloride fumes.
Why is this called a substitution reaction?
In CH₄ + Cl₂ → CH₃Cl + HCl, one H atom in methane is substituted by one Cl atom.
- High temperature
- Sunlight or UV light — correct
- A metal catalyst
- It turns limewater milky
- It produces white fumes with ammonia — correct
- It relights a glowing splint
- Atoms are added to the molecule
- One atom is replaced by another — correct
- The molecule splits into smaller parts