Question

Which of the following step is exothermic?

Answer 1

The correct answer is Na⁺  + Cl^- → NaCl

• The extra energy from the ions is released as heat when ionic bonds form. 
• When more heat is released from a reaction than is needed for it to happen, the reaction is exothermic.
• At the first step in the formation of NaCl, the solid Na should be converted to gaseous Na by the process sublimation so there comes sublimation entalpy, secondly the gaseous Na should lose one electron to become a Na⁺ ,so there comes the role of ionisation entalpy and if we see the case of chlorine molecule at first they need to dissociate to 2Cl and of electron affinity they should get an electron becoming stable.
•  At last we need to bring both of them to an equilibrium position such that the released energy is sufficient for them to make a bond (lattice energy) then in the same Na⁺ and Cl^- ions the electron and the protons in the nucleus attract so some energy is again spend against that. 
• Thus while looking overall we can under that the process of formation of NaCl is an exothermic process