IB Chemistry HL 1.2.2 Hess's law Question Bank

Practise IB Chemistry HL 1.2.2 by applying hess's law to exam-style questions.

Exam points

identify the relevant chemical structure, process or evidence
apply the correct chemical model or equation
evaluate the result using chemical reasoning and data

[Maximum number: 3]

Solid ionic compounds form crystal lattices.

(a)

Entalpy of solution, enthalpy of hydration and lattice enthalpy are related in an energy cycle.

[ 3 ]

(i)

Annotate the energy cycle for the enthalpy of solution of solid magnesium chloride, $\mathrm{MgCl}_{2}$ (s), by naming the processes A, B and C and completing the boxes. Include state symbols.

Figure for Question (i) — IB Chemistry HL

A:
B:
C:

[ 2 ]

Figure for Answer to Question (i) — IB Chemistry HL

Official Born-Haber/enthalpy cycle labels shown in the figure.

Correct boxes:
- A: enthalpy of solution / $\Delta H$ solution / $\Delta H_{\text{sol}}$ .
- B: lattice enthalpy / $\Delta H_{\text{lattice}}$ .
- C: enthalpy of hydration / $\Delta H_{\text{hydration}}$ .

(ii)

Calculate the enthalpy of solution for magnesium chloride, $\mathrm{MgCl}_{2}$ . Use sections 18 and 20 of the data booklet.

[ 1 ]

$\Delta H_{\text{solution}}=\Delta H_{\text{lattice}}+\Delta H_{\text{hydration}}$ $\Delta H_{\text{solution}}=2540+(-1963)+2(-359) =-141\ \mathrm{kJ\ mol^{-1}}$

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1.2.2—Hess's law question 1

Question (a)

Question (i)

Question (ii)