Question

The correct order hydration energy of alkali is:
A. $L{i^ + } > N{a^ + } > {K^ + } > R{b^ + }$
B. $R{b^ + } > {K^ + } > N{a^ + } > L{i^ + }$
C. $N{a^ + } > {K^ + } > L{i^ + } > R{b^ + }$
D. ${K^ + } > R{b^ + } > N{a^ + } > L{i^ + }$

Answer 1

Hint: Hydration energy is the heat energy when new bonds are made between the ions and water molecules known as the hydration energy. In alkali metals the hydration enthalpy decreases which increases the ionic size. If the element is in small size among all alkali metals, which has high charge density and the highest hydration energy of all the alkali metals.

Complete step by step answer:
The size is matter to define the hydration energy. The energy released as a result of the formation of new bonds between ions and water molecules which is called hydration energy. Increasing atomic number increases the size of the element which in turn outweighs increasing nuclear charge.
In alkali metals the hydration enthalpies decreases with increase the ionic sizes given as below:
 $L{i^ + } > N{a^ + } > {K^ + } > R{b^ + }$

Hence, option (A) is the correct answer.

Additional information:
Hydration enthalpy is defined by the size of elements; it is depending upon ionic potential which increases hydration enthalpy. Hydration enthalpies are always negative. Enthalpy is a measure of the energy released when attractions are kept up between positive or negative ions and water molecules.

Note: Alkali metals have high thermal and electrical conductivity and molality that are characteristic metals. Each alkali metal has a single electron in its outermost shell. It depends on the ionic potential. If potential is increased, hydration energy is also increasing.