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 <u>sublimation</u>.
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 <u>enthalpy of atomization or bond dissociation enthalpy.</u>
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 <u>ionization energy.</u>
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 <u>electron affinity.</u>
Therefore, it is an exothermic process.
5) Cs⁺(g) + Cl⁻(g) → CsCl(s<u>)</u>
This step involves the formation of solid crystal directly from the gas by the release of energy. This process is known as <u>crystallisation</u>.
It is an exothermic process.
