CAIE A-Level Chemistry A2 23.1 Lattice Energy and Born Haber Cycles Questions

Practise defining lattice energy and constructing cycles from atomisation, ionisation and electron-affinity steps.

Exam points

define lattice energy for formation of one mole of ionic solid from its gaseous ions
place every element, atom, gaseous ion and electron at the correct level with state symbols
apply Hess’s law with correct stoichiometric multipliers and signs to solve a missing enthalpy

Covered syllabus points

23.1.1—Terms 23.1.2—Terms: first electron affinity, EA 23.1.3—Born–Haber cycles for ionic solids 23.1.4—Calculations: Born–Haber cycles 23.1.5—Explain, in qualitative terms, the effect

[Maximum number: 4]

Potassium chloride, KCl , and magnesium chloride, $\mathrm{MgCl}_{2}$ , are both ionic solids.

Table 1.1

(a)

Explain the reasons why the lattice energy of $\mathrm{MgCl}_{2}$ is more exothermic than the lattice energy of KCl.

[ 2 ]

$\quad \mathrm{Mg}^{2+}$ is smaller (than $\mathrm{K}^{+}$ )

- $\mathrm{Mg}^{2+}$ is greater charge (than $\mathrm{K}^{+}$ )

- greater attraction

between $\mathrm{Mg}^{2+}$ and $\mathrm{Cl}^{-} /$ between the ions (in $\mathrm{MgCl}_{2}$ )

OR stronger ionic bonds (in $\mathrm{MgCl}_{2}$ )

(b)

Define the following terms.

[ 2 ]

(i)

enthalpy change of atomisation

[ 1 ]

(ii)

first electron affinity

[ 1 ]

[Maximum number: 6]

(a)

Calcium metal reacts with chlorine gas to form calcium chloride, $\mathrm{CaCl}_{2}$ .

[ 6 ]

(i)

Write an equation, including state symbols, to represent the lattice energy of calcium chloride, $\mathrm{CaCl}_{2}$ .

[ 1 ]

$\mathrm{Ca}^{2+}(\mathrm{g})+2 \mathrm{Cl}^{-}(\mathrm{g}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{~s})$ (state symbols required)

(ii)

Complete a fully labelled Born-Haber cycle that could be used to calculate the lattice energy, $\Delta H_{\text {latt }}^{\ominus}$ , for calcium chloride.

Figure for Question (ii) — CAIE A-Level Chemistry A2

[ 2 ]

(iii)

Use your answer to (ii) and the following data, together with relevant data from the Data Booklet, to calculate a value for $\Delta H_{\text {latt }}^{\ominus}$ for calcium chloride.

Table for Question (iii) — CAIE A-Level Chemistry A2

\Delta H_{\text {latt }}^{\ominus}=\ldots \ldots \ldots \ldots \ldots . . . . . . . . . . . . . . . . . . . . k J ~ m o l-1 ~

[ 3 ]

$\Delta \mathrm{H}_{\text {latt }}{ }^{\theta}=-796-242-178-590-1150+(2 \times 349)=-2258 \mathrm{~kJ} \mathrm{~mol}^{-1}$

[Maximum number: 2]

Potassium iodide, KI, is used as a reagent in both inorganic and organic chemistry.

Table 1.1 gives some data about the halide ions, $\mathrm{Cl}^{-}, \mathrm{Br}^{-}$ and $\mathrm{I}^{-}$ , and their potassium salts.

Table 1.1

The ionic radius of $\mathrm{Pb}^{2+}$ is 0.120 nm compared to 0.133 nm for $\mathrm{K}^{+}$ .

Suggest how the $\Delta H_{\text {latt }}^{\ominus}$ of $\mathrm{PbI}_{2}(\mathrm{~s})$ differs from $\Delta H_{\text {latt }}^{\ominus}$ of KI(s).
Explain your answer.

$\mathrm{Pb}^{2+}$ has a greater charge

- $\mathrm{Pb}^{2+}$ is smaller (than $\mathrm{K}^{+}$ ) $\mathbf{OR}\left(\mathrm{Pb}^{2+}\right)$ smaller ionic radius

- greater attraction between $\mathrm{Pb}^{2+}$ and $\mathrm{I}^{-}$

OR ionic bond between $\mathrm{Pb}^{2+}$ and $\mathrm{I}^{-}$ is stronger

OR lattice energy is more exothermic / more negative

mark as •

[Maximum number: 1]

Potassium chloride, KCl , and magnesium chloride, $\mathrm{MgCl}_{2}$ , are both ionic solids.

Table 1.1

Define the following terms.

enthalpy change of atomisation

[Maximum number: 1]

Potassium chloride, KCl , and magnesium chloride, $\mathrm{MgCl}_{2}$ , are both ionic solids.

Table 1.1

Define the following terms.

first electron affinity

[Maximum number: 2]

Calcium metal reacts with chlorine gas to form calcium chloride, $\mathrm{CaCl}_{2}$ .

Complete a fully labelled Born-Haber cycle that could be used to calculate the lattice energy, $\Delta H_{\text {latt }}^{\ominus}$ , for calcium chloride.

Figure for Question 6 — CAIE A-Level Chemistry A2

[Maximum number: 3]

Calcium metal reacts with chlorine gas to form calcium chloride, $\mathrm{CaCl}_{2}$ .

Use your answer to (ii) and the following data, together with relevant data from the Data Booklet, to calculate a value for $\Delta H_{\text {latt }}^{\ominus}$ for calcium chloride.

Table for Question 7 — CAIE A-Level Chemistry A2

\Delta H_{\text {latt }}^{\ominus}=\ldots \ldots \ldots \ldots \ldots . . . . . . . . . . . . . . . . . . . . k J ~ m o l-1 ~

$\Delta \mathrm{H}_{\text {latt }}{ }^{\theta}=-796-242-178-590-1150+(2 \times 349)=-2258 \mathrm{~kJ} \mathrm{~mol}^{-1}$

All question bank results loaded

Covered syllabus points

Question 1

Question (a)

Question (b)

Question (i)

Question (ii)

Question 2

Question (a)

Question (i)

Question (ii)

Question (iii)

Question 3

Question 4

Question 5

Question 6

Question 7