The enthalpy change for the following process would be expected to be a negative for — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Let's check the enthalpy change (ΔH) of each process:<br>(a) Na+(g) + e- → Na(g): This is the reverse of ionization of sodium. Since ionization is endothermic, the reverse capture of an electron by a positive gaseous ion is exothermic (ΔH < 0).<br>(b) F(g) + e- → F-(g): This represents the electron gain enthalpy of fluorine, which is highly exothermic (ΔH < 0) because fluorine has a strong affinity for electrons to complete its octet.<br>(c) Na+(g) + F-(g) → NaF(s): This represents the formation of a solid crystal lattice from gaseous ions (the reverse of lattice enthalpy). Since lattice formation is highly exothermic, ΔH < 0.<br>(d) $H_2O$(l) → $H_2O$(g): This is vaporization, which is always endothermic (ΔH > 0) as heat is absorbed to overcome intermolecular forces.<br>Thus, the processes with negative enthalpy changes are A, B, and C.