Question

What reaction takes place between Cesium and water that makes it react so violently?

Answer 1

Hint: To solve the above question, we should have information about alkali metals, Ionization enthalpy, Sublimation energy, and hydration enthalpy. Alkali metals are the most electropositive metal among the whole table. Here, reactivity increases down the group with lithium being the least and Caesium the most reactive element.
Ionization enthalpy is the energy provided to release one valence electron from the outer shell of the isolated gaseous atom. Sublimation enthalpy is the amount of heat required to change $ 1 $ mole of a substance at a solid-state to the gaseous state without undergoing a liquid state.
Hydration enthalpy is the amount of heat released when a substance undergoes hydration.

Complete step by step answer:
Step-1 :
All the alkali metals react with water vigorously with the production of metal hydroxide and the evolution of hydrogen gas. These metals are highly reducing in nature that is why they are water-reactive.
Step-2 :
When Caesium reacts with water, Caesium hydroxide is formed and hydrogen gas is evolved.
$ Cs(s) + H_2O(l) \rightarrow H_2(g) + CsOH(aq.) $
Here, and accounts for activation energy and hydration enthalpy decreases it.
Activation Energy = $ \delta H_{ sub } + I.E. - \delta H_{ hyd } $
Step-3 :
The sublimation and Ionization enthalpy is very small and hydration enthalpy is large in case of Caesium, So, the hydration enthalpy decreases the activation energy further helping in Caesium to react vigorously with water.

Note:
If we have to look towards the reaction and spontaneous or nonspontaneous nature of metals or elements, the formula for activation energy is remembered, taking into account its sublimation, ionization, and hydration enthalpy.