Question

Assertion :When a salt such as NaCl dissolves, the $N{a}^{+}$ and $C{l}^{-}$ ions leaving the crystal lattice acquire far greater freedom. Reason: In thermodyanamic terms, the formation of solution occurs with a favourable change in free energy, i.e. $△H$ has a high positive value and $T△S$ a low negative vaiue.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is C Assertion is correct but Reason is incorrect

In $NaCl$ crystal $N{a}^{+}$ and $C{l}^{-}$ are strongly bonded due to electrostatic attraction. As it is dissolved in solvent, $N{a}^{+}$ and $C{l}^{-}$ acquire greater freedom. In thermodynamic terms formation of solution occurs with a favourable change in $△G$. $T△S$ is largely $-ve$ which overcomes the small $+ve$ value of $△H$. Thus $△G$ is negative for dissolution of salt. Hence assertion is true but reason is false.