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 TypeSpontaneous process. A process which has a natural tendency to take place either by itself or after initiation under a given set of conditions is known as a spontaneous process. For example,
(i) Sugar dissolve in water and forms a solution.
Sugar + water 
Solution of sugar in water
(ii) In the domestic oven, coal keeps on burning once ignited.
Non-spontaneous process: A process that has no natural tendency or urge to take place is called non-spontaneous process. However, many non-spontaneous processes can also be made to take place by supplying energy continuously from some external sources. For example:
(i) Water can be made to flow uphill by the use of an electric motor pump.
(ii) Electrolysis of water to separate it into pure hydrogen and pure oxygen.
The tendency of a system to acquire a state of maximum randomness is the sole criterion for the spontaneity of a process. Comment.
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