How much energy is evolved when 2.75 mg of Cl (g) atoms adds electrons to give Cl- (g) ions? Electron affinity (Cl) = -349kJ/mol?

Molar mass of Cl = 35.5 g/mol
No. of moles of Cl atom = (2.75 g) / (35.5 g/mol) = 2.75/35.5 mol

Cl(g) + e⁻ → Cl⁻(g) …. ΔH = E.A. = -349 kJ/mol
When 1 mole of Cl(g) atoms form 1 mole of Cl⁻(g), 349 kJ of energy is evolved.

Energy evolved when 2.75 g Cl(g) atoms are used = (349 kJ/mol) × (2.75/35.5 mol) = 27.0 kJ