A2 1 Topic 1 & 2 Test Review

Which one of the following equations represents the lattice enthalpy of calcium bromide?

• Ca(s) + Br₂(l) → CaBr₂(s)

• CaBr₂(s) → Ca(s) + Br₂(g)

• Ca²⁺(g) + 2Br⁻(g) → CaBr₂(g)

• CaBr₂(s) → Ca²⁺(g) + 2Br⁻(g)

Using the values below calculate the lattice enthalpy of calcium chloride. First ionisation energy of calcium: +590 kJ mol⁻¹ Second ionisation energy of calcium: +1146 kJ mol⁻¹ Enthalpy of atomisation of calcium: +190 kJ mol⁻¹ Bond enthalpy of chlorine: +242 kJ mol⁻¹ Electron affinity of chlorine: -348 kJ mol⁻¹ Enthalpy of formation of calcium chloride: -795 kJ mol⁻¹

• +2615 kJ mol⁻¹

• +2267 kJ mol⁻¹

• +2276 kJ mol⁻¹

• +2509 kJ mol⁻¹

The lattice enthalpy of calcium chloride = +2267kj/mol. Use the enthalpies of hydration given below to determine the enthalpy of solution of calcium chloride. ΔHhyd(Ca²⁺) = -1651 kJ mol⁻¹ ΔHhyd(Cl⁻) = -364 kJ mol⁻¹

• +112 kJ mol⁻¹

• +252 kJ mol⁻¹

• -112 kJ mol⁻¹

• -252 kJ mol⁻¹

Using the data below, calculate the lattice enthalpy for magnesium chloride. First ionisation energy of magnesium: +738 kJ mol⁻¹ Second ionisation energy of magnesium: +1451 kJ mol⁻¹ Enthalpy of atomisation of magnesium: +148 kJ mol⁻¹ Enthalpy change of formation of magnesium chloride: -641 kJ mol⁻¹ Enthalpy of atomisation of chlorine: +121 kJ mol⁻¹ Electron affinity of chlorine: -348 kJ mol⁻¹

• +2524 kJ mol⁻¹

• +3000 kJ mol⁻¹

• +2000 kJ mol⁻¹

• +1500 kJ mol⁻¹

Explain what is meant by the term lattice enthalpy.

• Enthalpy change when one mole of an ionic compound is converted into gaseous ions

• Enthalpy change when one mole of a covalent compound is converted into gaseous ions

• Energy required to break one mole of covalent bonds in gaseous molecules

• Energy change when one mole of a substance is dissolved in water

Calculate the value, and give units of ΔS, for the following reaction at 25ºC. CaO (s) + H2O → Ca(OH)2 (s) (ΔG = -55.2 kJmol⁻¹ ΔH = -65.2 kJ mol⁻¹)

• S = -0.0336kJ K⁻¹mol⁻¹ or -33.6 J K⁻¹ mol⁻¹

• S = 0.0336kJ K⁻¹mol⁻¹ or 33.6 J K⁻¹ mol⁻¹

• S = -0.0536kJ K⁻¹mol⁻¹ or -53.6 J K⁻¹ mol⁻¹

• S = 0.0536kJ K⁻¹mol⁻¹ or 53.6 J K⁻¹ mol⁻¹

The entropy change (ΔS) is positive for the dissolution of an ionic solid in water because:

• The ions become more ordered in solution.

• The ions become less ordered in solution.

• The water molecules become more ordered around the ions.

• The water molecules become less ordered around the ions.

Calculate the temperature at which a reaction for which the enthalpy change (ΔH) is +100 kJ mol⁻¹ and the entropy change (ΔS) is + 0.04 kJK⁻¹ mol⁻¹ would become energetically feasible. Explain the reasoning behind your calculation.

• Temperature = 2500 K

• Temperature = 2000 K

• Temperature = 3000 K

• Temperature = 1500 K