Trouton’s rule

Trouton s rule The latent heat of vaportza lion (A/fvap) of liquid of molecular weight (A/) and boiling point (7 K) are related by the expression... 

The quantity zoi will depend very much on whether adsorption sites are close enough for neighboring adsorbate molecules to develop their normal van der Waals attraction if, for example, zu is taken to be about one-fourth of the energy of vaporization [16], would be 2.5 for a liquid obeying Trouton s rule and at its normal boiling point. The critical pressure P, that is, the pressure corresponding to 0 = 0.5 with 0 = 4, will depend on both Q and T. A way of expressing this follows, with the use of the definitions of Eqs. XVII-42 and XVII-43 [17] ... 

Enthalpy of Vaporization (or Sublimation) When the pressure of the vapor in equilibrium with a liquid reaches 1 atm, the liquid boils and is completely converted to vapor on absorption of the enthalpy of vaporization ISHv at the normal boiling point T. A rough empirical relationship between the normal boiling point and the enthalpy of vaporization (Trouton s rule) is ... 

A great many liquids have entropies of vaporization at the normal boiling point in the vicinity of this value (see benzene above), a generalization known as Trouton s rule. Our interest is clearly not in evaporation, but in the elongation of elastomers. In the next section we shall apply Eq. (3.21) to the stretching process for a statistical—and therefore molecular—picture of elasticity. 

By analogy with Trouton s rule we may expect that ... 

Transition, 19, 309, 461, 487 Trevelyan rocker, 25 Triple point, 214, 252 Trouton s rule, 234 True equilibrium, 90... 

Table 7.1 lists the standard entropies of vaporization of a number of liquids. These and other data show a striking pattern many values are close to 85 J-K 1-mol h This observation is called Trouton s rule. The explanation of Trouton s rule is that approximately the same increase in positional disorder occurs when any liquid is converted into vapor, and so we can expect the... 

Self-Test 7.7A Use Trouton s rule to estimate the standard enthalpy of vaporization of liquid bromine, which boils at 59°C. 

The normal boiling point of methanol is lower than predicted by Trouton s rule. Provide a molecular interpretation for this observation. 

Trouton s rule The empirical observation that the entropy of vaporization at the boiling point (the enthalpy of vaporization divided by the boiling temperature) is approximately 85 J-K—1 -mol 1 for many liquids. 

According to Trouton s rule, the entropy of vaporization of an organic liquid is a constant of approximately 85 J-mol 1 -K 1. The relationship between entropy of fusion, enthalpy of fusion, and melting point is given by... 

ASfus° = 9.79 J-K for Na ASfus° = 7.12 J-K. These numbers are reasonably close but clearly much smaller than the value associated with Trouton s rule. 

A very rough estimate can be obtained from Trouton s rule (Trouton, 1884), one of the oldest prediction methods. 

As was described in Chapter 6, the entropy of vaporization is a worthwhile piece of evidence in studying the association that occurs in liquids and vapors. In the case of [A1(C2H5)3]2, the entropy of vaporization (176.6 J mol-1 KT1) is almost exactly twice the value of 88Jmol-1K-1 predicted by Trouton s rule,... 

This indicates that in the process of vaporization 1 mole of liquid is converted into 2 moles of vapor. Therefore, we conclude that [Al(C2ff5)3]2 dimers are present in the liquid, but the vapor consists of monomeric Al(C2ff5)3 units. Examination of the data for [Al(Cff3)3]2 shows an entropy of vaporization of 112.61 mol 11<, which is greater than the value of 881 mol-1 K 1 predicted by Trouton s rule, but it is lower than twice the value. This value could be interpreted as corresponding to a liquid that is only partially dimerized being converted completely into monomer during vaporization. 

Trouton s rule is obeyed most closely by liquids that do not have a high degree of order within the liquid. In both HF and CH3OH, hydrogen bonds create considerable order within the liquid. In C6H5CH3, the only attractive forces are non-directional London forces, which cause the molecules to attract each other, but have no preferred orientation as... 

If we wish to know the enthalpy of formation of liquid Se2Cl2, we can estimate the enthalpy of condensation (perhaps from Trouton s rule [13] or by comparison with related sulfur compounds) and can add it to the value of A// , obtained in Equation (4.49). 

Trouton s rule phys chem An approximation rule for the derivation of molar heats of vaporization of normal liquids at their boiling points. traCit anz. riil ) true condensing point See critical condensation temperature. trii kan dens ir). point) true electrolyte puys chem A substance in the solid state that consists entirely of ions. trir i lek-tr9,lTt)... 

Vapour pressure. Vapour pressure (vp) of non associated liquids can be related to temperature (T) using the impirical equation of McGowan (35) which is based on a combination of Trouton s rule and the Clapeyron-Clausius equation as follows -... 

Repulsive forces determine, for example, the melting point of a solid. Whenever the packing is efficient, the melting point tends to be high. The attractive forces, on the other hand, govern the heat of vaporization and therefore the boiling point. Trouton s rule, which relates the normal boiling point of a liquid to its heat of vaporization, is a manifestation of this relation. 

Trouton s rule states that for most normal liquids the entropy of vaporization per mole 21 e.u. By a normal liquid, we mean which is not associated. In general association in the liquid state may be expected when intermolecular forces of a dominant type operate. Dipole moments, hydrogen bonding etc., lead to this situation. Abnormally high boiling points are a consequence of molecular association in the liquid state. 

The degree of association of molecules in a liquid can be estimated by means of its Trouton constant (Nash, 1984). At the normal boiling temperature, Tpp, vaporization proceeds with standard molar changes of enthalpy, AH%, and entropy, AS°bp, from which Trouton s rule is derived as given in eqn. 3.10. 

The entropy, Spontaneous vs non-spontaneous, Reversible and irreversible processes, Calculation of entropy changes (Isothermal, isobaric, isochoric, adiabatic), Phase changes at equilibrium, Trouton s rule, Calculation for irreversible processes... 

For liquid chlorine, M. Pellaton 22 found the value of f in J. D. van der Waals equation log (pefp) =f TcjT—1) is nearly 2 5 the ratio of the critical density to that calculated by the formula of a normal gas Z>=Mpc/22412(l-fa (.), namely 0 15765 3 635=DC/D and an application of Trouton s rule, 67 5 X70 92-y238 5 gives 20 67. Each of these three values is characteristic of what is obtained with non-associated liquids. 

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