CAIE A Level Chemistry 9701 · Reaction kinetics

Reaction kinetics: explain question

Explain6 marksChallenge

A reaction between two gases, $\ce{A(g)}$ and $\ce{B(g)}$ , takes place in a closed container at constant temperature. The concentration of $\ce{A}$ is halved while the concentration of $\ce{B}$ is kept constant.

Explain, in terms of collisions, why the rate of reaction decreases.

How this question is marked

6 marks, so the mark scheme is looking for about 6 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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