Calculate the free energy change when 1 mole of NaCl is dissolved in water at 298 K. (Given : Lattice energy of NaCl `= -777.8 kJ mol^(-1)`), Hydration energy `-774.1 kJ mol^(-1)` and `Delta S = 0.043 kJ mol^(-1) mol^(-1)` at 298 K).

Explanation

`Delta H` - Hydration energy - Lattice energy
`Delta H = -774.1 kJ mol^(-1) (-777.8 kJ mol^(-1)) = 3.7 kJ mol^(-1)`
`Delta G = Delta H - T Delta S = +3.7 kJ - 298 xx 0.043 kJ = +3.7 kJ - 12.81 kJ`
`Delta G = -9.11 kJ mol^(-1)`.