Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

(a)[3]

Predict and explain how the enthalpy change of hydration varies for the ions $\text{Na}^+$, $\text{Mg}^{2+}$ and $\text{Al}^{3+}$.

(b(i))[1]

Fig. 2.1 contains an incomplete energy cycle. Finish line C on Fig. 2.1. Include state symbols.

(b(ii))[2]

Identify change 2 on Fig. 2.1 using both words and symbols. Follow changes 1 and 3 as models for how this should be shown.

(b)

Fig. 2.1 contains an incomplete energy cycle.

(b(iii))[3]

Calculate a value for the lattice energy of magnesium chloride, $\Delta H_{\text{latt}}\, \text{MgCl}_2(s)$, by choosing and using suitable data from Table 2.1.

(c)[1]

Define entropy in terms of particle arrangements and energy distribution.

(d)[2]

At $25\,^{\circ}\text{C}$, the enthalpy change of solution for compound $Z$ is $+26\,\text{kJ mol}^{-1}$. At the same temperature, the entropy change of solution of $Z$ is $+52\,\text{J K}^{-1}\text{ mol}^{-1}$. Calculate the Gibbs free energy change, $\Delta G$, for the solution of $Z$ at $25\,^{\circ}\text{C}$.

(e(i))[1]

Use your answer to (d) to predict whether or not $Z$ is soluble in water at $25\,^{\circ}\text{C}$. Explain your answer.

(e(ii))[1]

Predict whether $Z$ becomes more or less soluble as the water temperature rises from $25\,^{\circ}\text{C}$ to $95\,^{\circ}\text{C}$. Explain your answer.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: $\Delta H_{hyd}$ becomes more negative from left to right because the ionic charge is higher

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