Radical substitution of alkanesEdexcel A-Level Chemistry: Flashcards
What these 12 flashcards ask
- What is a radical?
- What is homolytic fission?
- What conditions does the reaction of an alkane with a halogen need?
- What is the overall equation for methane reacting with chlorine to give chloromethane?
- What happens in the initiation step?
- Write the two propagation steps for methane and chlorine.
- What is a propagation step?
- What is a termination step?
- Give three termination steps for methane and chlorine.
- Why does radical substitution give a mixture of products?
- Which further products can form from chloromethane?
- How can further substitution be reduced?
Exam questions on Radical substitution of alkanes
- 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
- 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
- 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
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).