CAIE A Level Chemistry 9701 · Chemical energetics
A mixture of and can be kept at room temperature for a long time without reacting. When a spark is passed through the mixture, a vigorous exothermic reaction occurs, forming . Explain these observations in terms of the enthalpy change of the reaction and the activation energy.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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