Question

Which among the following salts dissolves in water with the absorption of heat?

• A. $Na_2SO_4$
• B. $CaCl_2$
• C. $Li_2SO_4.H_2O$
• D. $KCl$

Answer 1

Answer: (D)

KCl

Answer 2

When a salt dissolves in water, the enthalpy change ($\Delta$H) of the process can be positive (endothermic) or negative (exothermic). An endothermic dissolution absorbs heat from the surroundings and thus cools the solution.

Among the given salts:

• $CaCl_2$ is well known to dissolve exothermically.
• $Li_2SO_4 \cdot H_2O$ (the hydrated form) releases considerable heat upon hydration due to the strong hydration of $Li^+$ ions.
• $Na_2SO_4$ generally dissolves with a release of heat (exothermic), though effects may vary with temperature.
• $KCl$ has a positive enthalpy of solution (approximately +17 kJ/mol), meaning it dissolves by absorbing heat from its surroundings.

Thus, KCl is the salt that dissolves in water with the absorption of heat.

KCl’s dissolution in water is endothermic ($\Delta$H > 0), as it absorbs heat making the solution cooler, unlike the exothermic dissolutions of the other salts.