Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

The lattice energies for three ionic compounds are listed below: $\text{LiF}(s)$: $-1022\, \text{kJ mol}^{-1}$ $\text{CaO}(s)$: $-3513\, \text{kJ mol}^{-1}$ $\text{SrO}(s)$: $-3310\, \text{kJ mol}^{-1}$
(a(i))[2]

What is meant by lattice energy?

(a(ii))[1]

Explain why the lattice energy of CaO is more exothermic than the lattice energy of LiF.

(a(iii))[1]

Use the data in the table to estimate approximate values for the lattice energies of magnesium oxide and barium oxide. $\Delta H_{\text{latt}}\, \text{MgO}(s) =$ ................. $\text{kJ mol}^{-1}$ $\Delta H_{\text{latt}}\, \text{BaO}(s) =$ ................. $\text{kJ mol}^{-1}$

(b(i))[1]

Write an equation for the reaction between $\text{BaO}$ and $\text{H}_2\text{O}$. Include state symbols.

(b(ii))[4]

State and explain how the solubilities of the hydroxides of the Group 2 elements change down the group.

(c)[3]

Use the data below and the relevant Data Booklet data to calculate the lattice energy of magnesium fluoride, $\text{MgF}_2(s)$. It may help to draw an energy cycle. Show your working. Electron affinity of $\text{F}(g) = -348\ \text{kJ mol}^{-1}$. Enthalpy change of atomisation of $\text{Mg}(s) = +147\ \text{kJ mol}^{-1}$. Enthalpy change of formation of $\text{MgF}_2(s) = -1102\ \text{kJ mol}^{-1}$. $\Delta H_{\text{latt}}\text{MgF}_2(s) =$ \ldots

(d(i))[2]

Define electron affinity.

(d(ii))[1]

The electron affinity of carbon, $\text{C}(g)$, is $-120\ \text{kJ mol}^{-1}$. Suggest an explanation for why the electron affinity of fluorine differs from that of carbon.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: energy released when 1 mole of an ionic compound forms

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