Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

(a(i))

Write equations, including state symbols, that define the C-Br bond energy in $\text{CH}_3\text{Br}$.

(a(ii))[3]

Write equations, with state symbols, that define the Al-Cl bond energy in $\text{AlCl}_3$.

(b(i))

Describe and explain the pattern in bond energies for the bonds in $\text{Cl}_2$, $\text{Br}_2$ and $\text{I}_2$.

(b(ii))[3]

Fluorine, $\text{F}_2$, does not follow this trend. Suggest a possible reason why.

(c(i))

Use data from the Data Booklet to calculate the enthalpy change for the following reaction: $\text{H}_2(g) + \text{X}_2(g) \rightarrow 2\text{HX}(g)$ when $\text{X} = \text{Cl}$ and when $\text{X} = \text{I}$. Give your answers in $\text{kJ mol}^{-1}$.

(c(ii))[5]

Use these results to describe and explain the pattern in the thermal stabilities of the hydrides of Group VII.

(d(i))

Bromine reacts with hot $\text{NaOH}(aq)$ to produce a solution that, on cooling, forms white crystals of compound A. A has the following percentage composition by mass: Na, 15.2; O, 31.8; Br, 53.0. The rest of the solution contains mostly $\text{NaBr}$, with a small amount of compound A. Calculate the empirical formula of A.

(d(ii))[4]

Construct an equation for the reaction between $\text{Br}_2$ and hot $\text{NaOH}(aq)$.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: $\text{CH}_3\text{Br(g)} \rightarrow \text{CH}_3\text{(g)} + \text{Br(g)}$

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