The standard enthalpies of formation for three hypothetical solid salts (P, Q, and R) and their respective aqueous ions are given in the table below (in kJ mol ⁻¹ ): Salt H_f^ ( Solid ) H_f^ ( Cation (aq)) H_f^ ( Anion (aq)) P -900 -400 -400 Q -500 -300 -250 R -700 -350 -360 What is the correct order of these salts from the most exothermic to the most endothermic standard enthalpy of solution?

Step-by-step solution

The standard enthalpy of solution ( H_ sol ^ ) for a salt is calculated using Hess's Law: H_ sol ^ = H_f^ ( Cation (aq)) + H_f^ ( Anion (aq)) - H_f^ ( Solid ) Calculating for each salt: For P: H_ sol ^ = (-400) + (-400) - (-900) = -800 + 900 = +100 kJ mol ⁻¹ For Q: H_ sol ^ = (-300) + (-250) - (-500) = -550 + 500 = -50 kJ mol ⁻¹ For R: H_ sol ^ = (-350) + (-360) - (-700) = -710 + 700 = -10 kJ mol ⁻¹ Comparing the values, the order from most exothermic (most negative) to most endothermic (most positive) is Q ( -50 )