CHEMISTRY · Single correct · AP · Chemistry · Thermochemistry · Thermochemistry
Problem
When solid CaCl2 is added to water, the temperature of the solution rises noticeably. Which statement is most consistent with this observation?
(a) The dissolution is endothermic because energy is required to break the ionic lattice of CaCl2; this energy is absorbed from the surroundings, causing the temperature rise.
(b) The dissolution is exothermic because the enthalpy of hydration of the ions is positive, so heat is released.
(c) The dissolution is exothermic because the intermolecular attractions formed during hydration are stronger than those broken, releasing energy to the surroundings.
(d) The dissolution is endothermic because the large (negative) lattice energy of CaCl2 dominates over hydration, requiring heat input.