Question

“Lithium ion has the smallest hydration enthalpy of all the alkali metals.” Answer
Whether the above statement is true or false. If true enter 1, else enter 0.

Answer 1

Hint: Enthalpy of hydrogen is the amount of energy released on dilution of one mole of gaseous ion.

Complete answer:
Hydration enthalpy can be considered as enthalpy of solvation with the solvent being water.
Hydration enthalpy is also called hydration energy and its values are always negative. For a chemical reaction,
\[{M^{Z + }}\left( g \right){\text{ }} + {\text{ }}m{H_2}O\;\;\; \to \;{M^{Z + }}\left( {aq} \right)\]
Where \[{M^{Z + }}\left( {aq} \right)\] represents ions surrounded by water molecules and
dispersed in the solution. As the atomic numbers increase so do the ionic size, leading to a decrease in absolute values of enthalpy of hydration. Smaller the cation, greater is the degree of hydration. Alkali metals easily lose 1 electron and therefore have high values of “oxidising potential” which means high tendency to get oxidised and hence, powerful reducing nature in aqueous medium. Since \[L{i^ + }\] is small in size among all alkali metals, it has high charge density and hence, the highest hydration energy of all the alkali metals.

Therefore the given statement in the question is false.

Note: Hydration enthalpy \[(\Delta {H_{Hyd}})\] is the change in enthalpy when one mole of gaseous ion under a standard condition of 1bar pressure dissolves in a sufficient amount of water to form an infinitely dilute solution (infinite dilution means a further addition of solute will not cause any heat change).