Mechanism of Monochlorination of Methane - Evidence Flashcards
What evidence is there for the mechanism of monochlorination of methane?
(5)
Reaction takes place when exposed to UV light (doesn’t work in the dark at room temperature)
For every photon of light absorbed, thousands of chloromethane molecules are formed
Ethane is found in the products
Adding a source of free radicals such as tetramethyl lead speeds up the reaction
Addition of an inhibitor such as oxygen slows down the reaction rate
List the evidence there is for the mechanism of monochlorination of methane.
(5)
UV light - not dark
Photon of light = thousands of product
Ethane
Tetramethyl -increased rate
Oxygen - slows down rate
Explain why the fact that the reaction takes place when exposed to UV light (not in the dark) is a source of evidence of the mechanism.
The effect of UV light suggests a free radical mechanism in which CL2 is broken down into two Cl free radicals by UV light
Explain why the fact that every photon of light absorbed gives of thousands of chloromethane molecules is a source of evidence of the mechanism
This suggest that a chain reaction is taking place
Explain why the fact that ethane is found in the products in a source of evidence of the mechanism.
Methyl free radicals must be present
Two methyl free radicals must be combining together to form ethane
Explain why the fact that adding a source of free radicals such as tetramethyl lead speeds up the reaction is a source of evidence of the mechanism
Only a mechanism involving free radicals would be affected by adding a substance that provides free radicals, i.e. that promotes the chain reaction
Explain why the fact that the addition of an inhibitor such as oxygen slows down the reaction rate is a source of evidence of the mechanism
This implies a chain reaction is taking place, i.e. the inhibitor is combining with free radicals to stop the chain formation
