Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

(a)[1]

Complete Table 8.1 by putting one tick (✓) in each row to show the sign of each kind of energy change under standard conditions.

(b)[1]

Define the enthalpy change of hydration.

(c)

Table 8.2 sets out several energy changes that can be used in the questions that follow.

(c(i))[3]

Use relevant data from Table 8.2 to work out the lattice energy, $\Delta H^{\circ}_{\text{latt}}$, of $\text{CaBr}_2(s)$. Drawing a labelled energy cycle may help. Show your working.

(c(ii))[2]

Use relevant data from Table 8.2 and your answer to (c)(i) to work out the standard enthalpy change of hydration, $\Delta H^{\circ}_{\text{hyd}}$, of $\text{Br}^-$. Drawing a labelled energy cycle may help. If you could not answer (c)(i), use $-2500\,\text{kJ mol}^{-1}$ as your value for $\Delta H^{\circ}_{\text{latt}}$ of $\text{CaBr}_2(s)$. This is not the correct value. Show your working.

(c(iii))[2]

The enthalpy change of hydration of the $\text{Br}^-$ ion is more negative than that of the $\text{I}^-$ ion. Explain why.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: lattice energy always negative; enthalpy of hydration always negative; enthalpy of solution either negative or positive

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