For the dissolution of solid potassium nitrate, three major energetic processes occur under standard conditions (1 bar, substances in their standard states):
• Breaking ionic interactions in the crystal: +34 kJ mol⁻¹ and −71 J mol⁻¹ K⁻¹
• Reorganization of liquid water around the emerging cavity: +6 kJ mol⁻¹ and +22 J mol⁻¹ K⁻¹
• Formation of ion–dipole interactions between water and the ions: −41 kJ mol⁻¹ and +112 J mol⁻¹ K⁻¹
(The first value in each bullet is the standard enthalpy contribution; the second value is the standard entropy contribution.) Assume the temperature is 298 K throughout.
Answer the following questions. Show all reasoning and include correct units.
(a) Determine the overall standard enthalpy change for the dissolution of potassium nitrate.
(b) Determine the overall standard entropy change for the dissolution. Express the final value in J mol⁻¹ K⁻¹.
(c) Using your answers to parts (a) and (b), calculate the standard free energy change for the dissolution at 298 K. Be sure any necessary unit conversions are handled explicitly.
(d) State whether the dissolution of potassium nitrate is spontaneous under these conditions and justify your answer based on the numerical value obtained in part (c).