Define lattice energy.
Calculate a value for the enthalpy change of solution of copper(II) chloride, $\text{CuCl}_2\text{(s)}$, using the data below. Data: enthalpy change of hydration of $\text{Cl}^-$ $= -378\ \text{kJ mol}^{-1}$; enthalpy change of hydration of $\text{Cu}^{2+} = -2099\ \text{kJ mol}^{-1}$; lattice energy of $\text{CuCl}_2\text{(s)} = -2824\ \text{kJ mol}^{-1}$.
The enthalpy change of hydration of $\text{Ca}^{2+}$ is $-1579\ \text{kJ mol}^{-1}$. Use the Data Booklet to suggest why the $\Delta H_{hyd}$ values for $\text{Ca}^{2+}$ and $\text{Cu}^{2+}$ differ so much.
Identify the substances produced at the anode and the cathode during electrolysis of saturated $\text{CaCl}_2\text{(aq)}$.
Calcium may be made by electrolysis of molten calcium chloride, $\text{CaCl}_2\text{(l)}$. Calculate the mass, in g, of Ca produced when a current of $0.75\ \text{A}$ passes through $\text{CaCl}_2\text{(l)}$ for $60$ minutes. [$A_r: \text{Ca},\ 40.1$].
Explain the meaning of the term entropy of a system.
Put one tick (✓) in each row of the table to indicate the sign of each entropy change, $\Delta S$, for NaCl dissolving in water and for water turning into ice.
The evaporation of one mole of water has a standard Gibbs free energy change, $\Delta G^\circ$, of $+8.6\ \text{kJ}$ at $25\ ^\circ\text{C}$. Sketch a graph to show how $\Delta G^\circ$ varies for this process between $25\ ^\circ\text{C}$ and $150\ ^\circ\text{C}$ at $101\ \text{kPa}$.
The reaction of A with B is feasible at low temperatures but not feasible at high temperatures. $A + B \rightleftharpoons C + D$. Deduce the signs of $\Delta H$ and $\Delta S$ for this reaction and explain the reason the feasibility changes with temperature.