Chemistry 9701 · AS & A Level · States of matter

States of matter — practice question

Chloramine, $\text{NH}_2\text{Cl}$, is used in drinking-water treatment to kill bacteria. Any excess chloramine present in the water is broken down by UV light. Free radicals are involved in this mechanism. The initiation step is shown as follows: $\text{NH}_2\text{Cl} \xrightarrow{\text{UV}} \cdot\text{NH}_2 + \cdot\text{Cl}$.
(a(i))[1]

What does the term free radical mean?

(a(ii))[1]

Suggest an equation for one possible termination step in this process. A possible propagation step is $\text{NH}_2\text{Cl} + \cdot\text{Cl} \rightarrow \cdot\text{NHCl} + \text{HCl}$.

(b(i))[1]

Draw the dot-and-cross diagram for $\text{NH}_2\text{Cl}$, using only outer electrons.

(b(ii))[1]

State the hybridisation of the nitrogen atom and suggest the $\text{H-N-Cl}$ bond angle in the $\text{NH}_2\text{Cl}$ molecule.

(c(i))[1]

Define what is meant by the term entropy.

(c(ii))[1]

Calculate the standard entropy change, $\Delta S^{\circ}$, for the reaction.

(c(iii))[1]

Calculate the standard enthalpy change, $\Delta H^{\circ}$, for the reaction.

(c(iv))[2]

Calculate the standard Gibbs free energy change, $\Delta G^{\circ}$, for this reaction at $298\,\text{K}$.

(c(v))[1]

Explain, with reference to $\Delta G^{\circ}$, why this reaction becomes less feasible when the temperature is higher.

(d)[4]

Compare the basicities of ammonia, ethylamine and phenylamine, and explain your answer.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: A species containing an unpaired electron

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