Question

These are physical properties of an element
(A) Sublimation enthalpy
(B) Ionisation enthalpy
(C) Hydration enthalpy
(D) Electron gain enthalpy
The total number of above properties that affect the reduction potential is _________. (Integer answer)

Hint:

The value of \(E^\circ\) depends on \(\Delta H = \Delta H_{sub} + \Delta H_{IE} + \Delta H_{hyd}\). Metals with very high negative hydration energies and low ionisation/sublimation energies tend to have very negative reduction potentials (e.g., Lithium).

Answer 1

Correct Answer: 3

Step 1: Understanding the Concept:
The standard electrode potential (reduction potential) of a metal electrode (\(M^{n+}/M\)) is determined by the enthalpy changes in a thermodynamic cycle (Born-Haber cycle for ions in solution).
Step 2: Detailed Explanation:
The process \(M^{n+}_{(aq)} + ne^- \rightarrow M_{(s)}\) can be broken down into:
1. Hydration of the ion: \(M^{n+}_{(aq)} \rightarrow M^{n+}_{(g)}\) (Reverse of hydration enthalpy)
2. Ionisation of gas atoms: \(M^{n+}_{(g)} + ne^- \rightarrow M_{(g)}\) (Reverse of ionisation enthalpy)
3. Atomisation/Sublimation: \(M_{(g)} \rightarrow M_{(s)}\) (Reverse of sublimation enthalpy)

Therefore, sublimation enthalpy, ionisation enthalpy, and hydration enthalpy are the three key factors that determine the reduction potential of metallic elements. Electron gain enthalpy is typically used for defining the oxidizing power of non-metals (like halogens) and is not part of the standard metal electrode potential cycle.
Step 3: Final Answer:
The total number of properties is 3.