Question

H$_2$O(s) H$_2$O(l) The correct set of sign of G, H and S respectively for the above given process is :

• A. +, +, +
• B. +, –, +
• C. –, +, +
• D. –, –, +

Answer 1

Answer: (C)

–, +, +

Answer 2

The process H$_2$O(s) $\rightarrow$ H$_2$O(l) represents the melting of ice.

1. Enthalpy Change ($\Delta H$): Melting is an endothermic process, meaning it requires energy input to overcome the intermolecular forces in the solid state. Therefore, $\Delta H$ is positive ($\Delta H > 0$).

2. Entropy Change ($\Delta S$): In the solid state (ice), molecules are arranged in an ordered crystalline structure. In the liquid state (water), molecules have greater freedom of movement and are less ordered. Thus, entropy increases during melting, and $\Delta S$ is positive ($\Delta S > 0$).

3. Gibbs Free Energy Change ($\Delta G$): The spontaneity of a process is determined by $\Delta G = \Delta H - T\Delta S$. For melting to occur spontaneously (i.e., at temperatures above the melting point), $\Delta G$ must be negative ($\Delta G < 0$). This happens when the $T\Delta S$ term is greater than $\Delta H$.

Therefore, the signs for $\Delta G$, $\Delta H$, and $\Delta S$ are –, +, + respectively.