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Enthalpy of Sublimation
Enthalpy of sublimation of a given substance is defined as the enthalpy change when one mole of the given substance in solid form is converted into vapour phase at the said temperature. One of the examples is
I2(s) I2(g)

According to Hess's law, the enthalpy of sublimation will be equal to sum of the enthalpy of fusion and enthalpy of vaporization, i.e.

Enthalpy of Neutralization
Enthalpy of neutralization is defined as the enthalpy change when one mole of H+ in dilute solution combines with one mole of OH- to give undissociated water, i.e.
H+(aq)+OH-(aq) → H2O(1)ΔHneut -57.3 kJ

In this reaction, there is always release of heat because of bond formation, H...OH. Whenever one mole of a strong monoprotic acid (HCl,HNO3) is mixed with one mole of a strong base (NaOH, KOH), the above neutralization reaction takes place, these acids and bases are present in the completely dissociated form in dilute solutions.

Enthalpy of Ionization
When a weak acid (or base) reacts with a strong base (or acid), the release of heat is less than 57.3 kJ. It is because of the fact that these acids or bases are not completely ionized in solution. Some of the heat is consumed in ionizing these acids and bases. This energy is known as enthalpy of ionization. Examples are
HCN + Na+OH- Na+CN+H2O  (ΔH° =-12.13 kJ)
 NaCH3COO- + H2O (ΔH°=-55.23 kJ)

Obviously, according to Hess's law
ΔH° = ΔH° ionic +Δ H° neut
ΔH° ionic = Δ H°ΔH°neut

ΔH° ionic (HCN)= -12.13 kJ - (-57.3 kJ)=45.17 kJ
ΔH° ionic (CH3COOH)=-55.23 kJ - (-57.3 KJ)
=2.07 kJ

Enthalpy of Transition
Enthalpy of transition is the enthalpy change when one mole of one allotropic form changes to another. For example,
C (graphite)  C (diamond) Δ H° = 1.90 KJ

Enthalpy of Solution
Enthalpy of solution may be defined as the enthalpy change when one mole of the solute is dissolved in a definite quantity of solvent to produce a solution of a particular concentration. A few examples are
MgSO4(g) + aq  MgSO4(aq) Δ H = - 91.2 KJ
MgSO4 H2O(s) + aq
 MgSO4(aq)ΔH = - 18.8 KJ
Where aq stands for a very large quantity of water. The resultant solution is known as infinite dilute solution.

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