Animated Solution for Chemistry - Electrochemistry: 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)

When we talk about the standard reduction potential (or oxidation potential) of a metal, we are essentially measuring its thermodynamic tendency to convert between its solid state and its aqueous ionic state. But this transformation, $M(s)\rightleftharpoons M^{n+}(aq)+n{e}^{-}$, is not a single magical leap. It is a journey that requires breaking down the process into fundamental, measurable thermodynamic steps using a Born-Haber cycle.

To understand the total energy change (${\Delta }_{\mathrm{total}}H$), we must walk the metal through three distinct physical phases:

1. Sublimation Enthalpy (${\Delta }_{\mathrm{sub}}H$): You cannot simply pluck an electron from a rigid metallic lattice. The first step is to isolate the metal atoms by converting the solid into a gas. This requires an input of energy known as the sublimation enthalpy.

2. Ionisation Enthalpy (${\Delta }_{i}H$): Once we have isolated gaseous atoms, we need to strip away the valence electrons to form gaseous cations. The energy required to overcome the nuclear attraction and remove these electrons is the ionisation enthalpy.

3. Hydration Enthalpy (${\Delta }_{\mathrm{hyd}}H$): Finally, these highly unstable gaseous ions are plunged into water. The polar water molecules surround the cation, forming strong ion-dipole interactions. This process releases a massive amount of energy, known as the hydration enthalpy. This exothermic step is often the driving force that makes the entire oxidation process feasible.

Notice that throughout this cycle for a metal, we are removing electrons to form cations. At no point does the metal atom gain an electron. Therefore, Electron Gain Enthalpy plays absolutely no role in determining the electrode potential of a metal.

The total enthalpy change is the sum of these three properties:

Thus, exactly 3 of the listed physical properties affect the reduction potential of the element.