CAIE A Level Chemistry 9701 · Hydrocarbons
Ethene can be converted into ethane by hydrogenation. Ethane can then undergo free-radical substitution with chlorine in the presence of ultraviolet light.
Describe how ethene is converted into ethane, and describe the mechanism of the reaction of ethane with chlorine, including the initiation, propagation and termination steps.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
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