Question

The formation of CsCl from Cs(s) and Cl2(g) involves the following steps:Cs(s)?Cs(g)12Cl2(g)?Cl(g)Cs(g)?Cs+(g)+e?Cl(g)+e??Cl?(g)Cs+(g)+Cl?(g)?CsCl(s)Which of these steps absorb energy and which release energy?

Answer 1

Answer:

The steps 1, 2 and 3 involve absorption of energy and steps 4, 5 involve release of energy.

Explanation:

The steps involved in the formation of caesium chloride (CsCl) are:

1) Cs(s) → Cs(g)

This step involves the phase transition of caesium from the solid phase to the gaseous phase, which is known as sublimation.

Sublimation is an endothermic process as it is caused by the absorption of energy.

2) Cl₂(g) → 2Cl(g)

This step involves breaking the Cl-Cl bond and the energy required for the separation of constituting atoms is called enthalpy of atomization or bond dissociation enthalpy.

Therefore, it also an endothermic process.

3) Cs(g) → Cs⁺(g) + e⁻

The energy needed for the removal of valence electron from the valence shell of gaseous caesium atom to form a cation is known as ionization energy.

It is also an endothermic process.

4) Cl(g) + e⁻ → Cl⁻(g)

The energy released when an electron is gained by a gaseous chlorine atom to form an anion is known as electron affinity.

Therefore, it is an exothermic process.

5) Cs⁺(g) + Cl⁻(g) → CsCl(s)

This step involves the formation of solid crystal directly from the gas by the release of energy. This process is known as crystallisation.

It is an exothermic process.