The lattice energy of NaCl is +788 kJ `mol^(-1).` The enthalpies of hydration of `Na^(+)`(g) and `Cl^(-)` (g) ions are `-406 kJ mol^(-1)and-378 kJ mol^(-1)` respectively. The enthalpy of solution of NaCl(s) in water is

Options

A. `786 kJ mol ^(-1)`
B. `4 kJ mol ^(-1)`
C. `-4 kJ mol ^(-1)`
D. `- 792 kJ mol ^(-1)`

Explanation

`N a Cl _((s)) to N a _((g)) ^(+) + C l _((g)) ^(-) " " Delta H = + 788 kJ` (Lattice energy)
`Na _((g)) ^(+) + H _(2) O _((l)) to Na _((aq))^(+)" " Delta H =- 406 kJ` (Hydration)
`Cl _((g)) ^(-) + H _(2) O _((l)) to Cl _((aq)) ^(-) " "Delta H =- 378 kJ `( Hydration)
The net reaction of dissoultion of `NaCl (s) is Na Cl _((s)) + 2 H _(2) O _((l)) to Na _((aq)) ^(+) + Cl _((aq)) ^(- )`
`Delta _(sol) H = 788 - ( 406 + 378) =- 4 kJ mol ^(-1)`