Write an equation for the decomposition of $\text{NaN}_3$.
Complete the dot-and-cross diagram for the azide ion, $\text{N}_3^-$. Apply the electron key that is provided.
Lattice energies are always negative, which shows that they are exothermic changes. Explain what is meant by the term lattice energy.
Explain why lattice energy is an exothermic change.
Use the data below and any relevant values from the Data Booklet to calculate the standard enthalpy change of formation, $\Delta H_f^\circ$, of $\text{NaN}_3(s)$. Give a sign in your answer. Show all of your working. Data: lattice energy, $\Delta H_{\text{latt}}^\circ$, of $\text{NaN}_3(s)$ is $-732\ \text{kJ mol}^{-1}$; standard enthalpy change of atomisation, $\Delta H_{\text{at}}^\circ$, of $\text{Na}(g)$ is $+107\ \text{kJ mol}^{-1}$; standard enthalpy change, $\Delta H^\circ$, for $\tfrac{1}{2}\text{N}_2(g) + e^- \rightarrow \text{N}_3^-(g)$ is $+142\ \text{kJ mol}^{-1}$. $\Delta H_f^\circ$ of $\text{NaN}_3(s) = \ldots\ldots\ldots\ \text{kJ mol}^{-1}$.
The lattice energy, $\Delta H_{\text{latt}}^\circ$, of $\text{RbN}_3(s)$ is $-636\ \text{kJ mol}^{-1}$. Suggest why the lattice energy of $\text{NaN}_3(s)$, $-732\ \text{kJ mol}^{-1}$, is more exothermic than that of $\text{RbN}_3(s)$.