Enthalpy of vaporisation

In the case of solids, the enthalpy of atomisation includes the enthalpies of fusion and vaporisation in the case of liquids, it includes the enthalpy of vaporisation. 

Substance Melting point (K) Enthalpy of crystallisation (kl/kg) Boiling point (K) Enthalpy of vaporisation (kJ/kg)... 

The effect of vapour pressure is most easily visualised when the rates of degradation are plotted as a function of the enthalpy of vaporisation (Fig. 5.14). Plainly the lower the enthalpy of vaporisation (Ai-f ), the more volatile the solvent and the more solvent vapour will enter the bubble. This effectively cushions the collapse of the bubble, so that the movement of solvent is slowed down, lessening the shock wave thereby leading to lower degradation rates. 

Fig. 5.14. The effect of the enthalpy of vaporisation on the degradation rate constant of dextran solutions. A - Water ...

Estimates for Cp were based on Hildebrand s solubility parameters, Sij, (Hildebrand and Scott 1950), which are related to the enthalpy of vaporisation and the... 

Fig. 12-3.—The enthalpies of vaporisation of isoelectronic sequences of hydride molecules.

Using the knowledge you have obtained from Chapter 1, p. 5, give a full definition of the enthalpy of fusion and enthalpy of vaporisation for water. 

Enthalpy of vaporisation The enthalpy change that takes place when one mole of liquid is changed to one mole of vapour at the same temperature. 

If bubbles of air 10 7 m in diameter and no other nuclei are present in water just below the boiling point, by approximately how much could water be superheated at normal atmospheric pressure before boiling starts The surface tension of water at 100°C is 59 mN mT1 and its enthalpy of vaporisation is 2.25 kJ g 1. 

Using the Clapeyron equation, calculate the enthalpy of vaporisation (evaporation) of water from the following data ... 

Atrs H° A vapH° standard enthalpy of transition per mole (between phases) standard enthalpy of vaporisation per mole A trsH°... 

A rule of thumb, called Trouton s Rule, approximates the enthalpy of vaporisation, Avap H° by ... 

When a liquid the enthalpy change taking place is called the enthalpy of vaporisation, AvapH°. Thus the corresponding change is ... 

From the above definition, the Gibbs energy and enthalpy of vaporisation, AvapG° and AvapH° respectively of the solvent at constant pressure are such that (for process 52.2) ... 

Thus the elevation of the boiling point, AZb, of a liquid (molar mass, Mm, boiling point, Tb and enthalpy of vaporisation, AvapH° at 1 bar pressure) caused by addition of zwSoiute can be calculated using equation (52.12). 

Enthalpy of Vaporisation It is the enthalpy change that accompanies the change of 1 mole of a liquid into vapour state completely at its boiling point, e.g.,... 

Entropy of Vaporisation (DSvap) The vaporisation of a substance occurs at a definite temp, (i.e., its b.p) and is accompanied by absorption of heat (enthalpy of vaporisation). The change in entropy known as entropy of vaporisation is given by... 

ASvapjn is equal to ratio between the molar enthalpy of vaporisation and the boiling temperature, which leads to Eq. (18.10). The molar enthalpy and entropy of vaporisation and the boiling temperature of some simple liquids are presented in Table 18.2 Some liquids deviate sharply from the rule. This is often because these liquids have structure and so a greater amount of disorder is introduced when they evaporate. Examples are water and methanol due to hydrogen bonds between the molecules. (Atkins and De Paula, 2006)... 

The value of the maximum dissociation energy in a homonuclear diatomic transition metal molecule has been predicted (2) to be (600 40) kJ mol-1 for ditantalum. The dissociation energies of homonuclear transition metal molecules have been predicted by various methods of which the most recent is the cell model of Miedema (7). This proposes a relation between the enthalpy of vaporisation of the solid metal, AH ap, the dissociation energy, D°, of the diatomic molecule and the surface energy of the metal, Y° as follows,... 

The following table shows the boiling point, Tb, of benzene and trichloromethane, along with their enthalpies of vaporisation ... 

For carbon dioxide the enthalpy of fusion Afus// is 8.3 0.1 kJ mol while the enthalpy of vaporisation Avap// is 16.9 0.2 kJ mol. In fact, carbon dioxide sublimes with the enthalpy of sublimation AsubT/ given by... 

---