Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

Under aqueous conditions, chlorate(I) ions react according to the equation below. $2\text{NH}_3 + \text{ClO}^- \rightarrow \text{N}_2\text{H}_4 + \text{Cl}^- + \text{H}_2\text{O}$ A set of experiments was performed using different concentrations of $\text{ClO}^-$ and $\text{NH}_3$. The table lists the outcomes.
(a(i))[2]

From the table, work out the order for each reactant, $\text{ClO}^-$ and $\text{NH}_3$. Make your reasoning clear.

(a(ii))[1]

State the rate equation for this reaction.

(a(iii))[2]

Calculate the rate constant, $k$, for this reaction using the data from experiment 1. Include the units for $k$.

(a(iv))[1]

On the axes, sketch a graph showing how $k$ varies as temperature is increased.

(b(i))[2]

Describe how the results from this experiment could be used to verify that the reaction is first-order with respect to $[\text{I}^-]$.

(b(ii))[1]

Using this mechanism, deduce the overall equation for this reaction.

(b(iii))[1]

Identify the step that contains a redox reaction. Explain your answer.

(iv)[1]

On the axes, sketch a graph showing how $k$ varies as temperature rises.

(b)

A further experiment examined the reaction between chlorate(I) ions and iodide ions in aqueous alkali. A solution containing iodide ions in aqueous alkali was added to a large excess of chlorate(I) ions, and $[\text{I}^-]$ was measured at regular intervals.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: When $[NH_3]$ is doubled, the rate becomes $\times4$; order $=2$

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