Radical substitution of alkanesEdexcel A-Level Chemistry: Mind map

Exam questions on Radical substitution of alkanes

1. A student places a mixture of methane and chlorine in a flask. Nothing happens in the dark, but the gases react quickly when the flask is exposed to ultraviolet light, forming chloromethane and hydrogen chloride.
   Explain why the mixture does not react in the dark but reacts when exposed to ultraviolet light.2 marks
2. A chemist exposes a mixture of ethane and bromine to ultraviolet light and obtains bromoethane, C₂H₅Br, and hydrogen bromide, HBr, by a radical chain reaction.
   Write the equations for the two propagation steps in the formation of bromoethane from ethane and bromine.2 marks
3. A mixture of methane and chlorine, with the methane in limited supply, is kept in ultraviolet light. Analysis of the product mixture shows chloromethane, dichloromethane, trichloromethane and a trace of ethane.
   Explain how the trace of ethane is formed in this reaction and why its formation stops the chain reaction.3 marks