Short Answer Type
Long Answer TypeHow can the lattice enthalpy of an ionic NaCl be determined by using Born-Haber cycle?
Calculate the lattice enthalpy of KCl crystal from the following data:
Sublimation enthalpy of pottasium (K) = +89 kJ mol-1
Dissociation enthalpy of 
= +122 kJ mol-1
Ionisation enthalpy of K(g) +425 kJ mol-1
Electron gain enthalpy of Cl(g) = -355 kJ mol-1
Enthalpy of formation of 
Calculate the lattice enthalpy of LiF, given that the enthalpy of
(i) sublimation of lithium is 155.2 kJ mol–1
(ii) dissociation of 1/2 mol of F2is 75.3 kJ
(iii) ionization of lithium is 520 kJ mol–1
(iv) electron gain of 1 mol of F(g) is –333 kJ
(v) ∆f H0 ∆fH0 overall is –795 kJ mol–1
Short Answer TypeCalculate the lattice enthalpy of MgBr2 from the given data. The enthalpy of formation of MgBr2 according to the reaction
Long Answer TypeThe tendency of a system to acquire a state of maximum randomness is the sole criterion for the spontaneity of a process. Comment.
No, there is a natural tendency of a system to attain a state of the greater randomness i.e. more disordered state. For example,
(i) There is more randomness on mixing of two gases (which do not react chemically).
(ii) Evaporation of water. The evaporation of water results in increase of randomness because the molecules in the vapour state have more randomness than in the liquid state
(iii) Dissolution of ammonium chloride in water. Solid ammonium chloride has less randomness while in solution ammonium chloride particles move freely as 
and hence randomness increases.
If the randomness factor were the only criterion, then the process like liquefaction of gas or solidification of a liquid would not have been feasible since these were accompanied by a decrease in randomness. Hence the tendency of a system to acquire a state of maximum randomness is not the sole criterion for determining the spontaneity of the process.
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