Question

When many atoms combine to form ionic compounds the reaction is highly exothermic. Where is most of this energy coming from?

		The energy released when the ions combine to form the ionic compounds.
		The energy released when atoms gain electrons to make the anions.
		The energy associated with formation of the cations.
		The energy associated with forming both the anion and the cation.

Answer 1

Ans :- Option (a) i.e. "The energy released when the ions combine to form the ionic compounds " is the correct answer.

Explanation :-

Following energies are involved during the formation of ionic bond .

(1). Lattice Enthalpy (deltaH_Lattice ) :- Amount of energy released when the ions (i.e. cation and anion ) combine to form the ionic compounds.

deltaH_Lattice = - ve (Released)

(2).Electron gain enthalpy (deltaH_eg ):- Amount of energy released when atoms gain electrons to make the anions.

deltaH_eg = - ve (Released)

(3). Ionisation energy (deltaH_i ) :- Amount of energy required for the formation of cation.

deltaH_i = + ve (Absorb)

But value of Lattice enthalpy is more negative than electron gain enthalpy therefore most of the energy coming from lattice enthalpy i.e. option (a).

Hence Option (a) is the correct answer.