A solid salt dissolves in water according to the following thermochemical equation: NaCl(s) → Na^+(aq) + Cl^-(aq); ΔH = +3.9 kJ/mol. Which statement correctly describes the enthalpy of solution for NaCl(s)?

• A. The enthalpy of solution is negative, indicating the process is exothermic.
• B. The enthalpy of solution is zero, indicating no heat is absorbed or released.
• C. The enthalpy of solution cannot be determined from the given equation.
• D. The enthalpy of solution is positive, indicating the process is endothermic.

Answer: (D)

Verified step by step guidance

1. Identify the thermochemical equation given: \(\mathrm{NaCl(s) \rightarrow Na^{+}(aq) + Cl^{-}(aq)}\) with \(\Delta H = +3.9\ \mathrm{kJ/mol}\).
2. Recall that \(\Delta H\) represents the enthalpy change of the process, which in this case is the enthalpy of solution (the heat change when one mole of NaCl dissolves in water).
3. Note the sign of \(\Delta H\): a positive value (\(+3.9\ \mathrm{kJ/mol}\)) means that heat is absorbed from the surroundings during the dissolution.
4. Understand that when \(\Delta H\) is positive, the process is endothermic, meaning the system takes in heat rather than releasing it.
5. Conclude that the enthalpy of solution for NaCl is positive, indicating the dissolution process is endothermic.