A student observes that dissolving MgCl₂ in water releases noticeably more heat than…
CHEMISTRY · Single correct · A Level · Chemistry · Bonding · Bonding
Problem
A student observes that dissolving MgCl₂ in water releases noticeably more heat than dissolving the same number of moles of NaCl under identical conditions. Which of the following best accounts for this difference?
(a) The lattice energy of MgCl2 is greater than that of NaCl, and the release of this extra lattice energy upon dissolution gives the larger temperature rise.
(b) Dissolving MgCl2 produces three ions whereas dissolving NaCl produces only two, so a greater number of ion–water interactions generates more heat.
(c) The Mg²⁺ ion has a greater charge and a smaller ionic radius than Na⁺, leading to stronger ion–dipole attractions with water and a more negative hydration enthalpy.
(d) The Mg–Cl bond is more polar than the Na–Cl bond, so breaking these bonds in water releases more energy in the case of MgCl2.