The dissolution of solid in water is endothermic

CHEMISTRY · Single correct · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

The dissolution of solid

\text{KNO}_3

in water is endothermic, yet the salt readily dissolves at

25\,^{\circ}\text{C}

. Which statement best accounts for the spontaneity of this process? (a) The hydration enthalpy released when the

\text{K}^+

and

\text{NO}_3^-

ions interact with water is large enough to make

\Delta H^{\circ}

negative, so

\Delta G^{\circ}

is negative. (b) At

25\,^{\circ}\text{C}

the term

T\Delta S^{\circ}

becomes negative and subtracts from the positive

\Delta H^{\circ}

, giving an overall negative

\Delta G^{\circ}

. (c) The large increase in the disorder of the ions and surrounding water molecules produces a positive

\Delta S^{\circ}

that outweighs the positive

\Delta H^{\circ}

, making

\Delta G^{\circ}

negative. (d) Because water is highly polar, ionic compounds dissolve spontaneously regardless of the signs of

\Delta H^{\circ}

and

\Delta S^{\circ}