CHEMISTRY · Single correct · A Level · Chemistry · Thermodynamics · Thermodynamics
Problem
Two salts are investigated at 25 °C.
• Salt Q: lattice energy +3,500 kJ mol⁻¹; hydration energy −3,200 kJ mol⁻¹
• Salt R: lattice energy +2,400 kJ mol⁻¹; hydration energy −2,500 kJ mol⁻¹
Based on these data, which salt is predicted to have the greater molar solubility in water, and why?
(a) Salt Q, because the calculated enthalpy of solution is −300kJ mol−1, making dissolution highly exothermic.
(b) Salt R, because the sum of its lattice and hydration energies is more negative than that of Salt Q, making dissolution more exothermic.
(c) Salt Q, because its hydration energy magnitude exceeds its lattice energy, giving a more favorable enthalpy of solution.
(d) Salt R, because its lower lattice energy means the crystal requires less energy to break apart in water.