Boiling Point of a Liquid at a Given Pressure

 

Steps:

(1) determine the entropy of vaporization of the liquid at the current temperature

(2) perform a first approximation for the difference in temperature from the current temperature to the boiling point under 760 mm Hg

(3) reach a first approximation of the boiling temperature under 760 mm Hg by adding the current temperature and the difference in temperature

(4) determine the entropy of vaporization for the liquid at the estimated boiling temperature under 760 mm Hg

(5) adjust the difference in temperature for the change in entropy of vaporization

(6) reach a second approximation of the boiling temperature under 760 mm Hg by adding the current temperature and the adjusted difference in temperature

Group	Chemicals
1	anthracene, anthraquinone, butylethylene, carbon monoxide, methane, methyl silicane, phenanthrene, trichlorethylene
2	benzaldehyde, benzonitrile, benzophenone, camphor, carbon oxysulfide, carbon suboxide, carbon sulfoselenide, dibenzyl ketone, dimethyl silicane, ethers, hydrocarbons, methyl ethyl ketone, methyl salicylate, nitrotoluene (o, m, p), nitrotoluidines (o, m, p), phosgene, phthalic anhydride, quinoline, sulfides
3	acetaldehyde, acetone, amines, chloroanilines (m, p), cyanogen chloride, esters, ethylene oxide, formic acid, hydrogen cyanide, methyl benzoate, methyl ether, methyl ethyl ether, methyl fluoride, naphthols, nitrobenzene, nitromethane, tetranitromethane
4	acetic acid, acetophenone, cresols (o, m, p), cyanogen, dimethyl amine, dimethyl oxalate, ethylamine, glycol diacetate, methyl formate
5	benzoic acid, benzyl alcohol, methyl amine, phenol, propionic acid
6	acetic anhydride, isobutyric acid, water
7	butyric acid, ethylene glycol, heptylic acid, isoamyl alcohol, isocaporic acid, methanol, valeric acid
8	n-amyl alcohol, ethanol, isobutyl alcohol, n-propyl alcohol

 

Derivatives:

(1) chlorinated: same group as if Cl were hydrogen

(2) halogenated: same group as if halogen were hydrogen

 

The graph on page D-193 showing entropy vs temperature for each group can be approximated by the following:

 

entropy of vaporization for current temperature at 760 mm Hg =

= ((slope for group) * (temperature in °C)) + (intercept for group)

 

Group	slope	intercept
1	0.00205	4.2995
2	0.00205	4.5415
3	0.00213	4.7671
4	0.00223	4.9953
5	0.00229	5.2183
6	0.00230	5.4378
7	0.00234	5.6658
8	0.00231	5.8977

 

estimated delta temperature =

= A / B

 

A =

= ((273.1 + (temperature for boiling liquid in °C)) * (2.8808 - log10(pressure when boiling in mm Hg)))

 

B =

= (entropy of vaporization at 760 mm Hg) + (0.15 * (2.8808 - log10(pressure when boiling in mm Hg)))

 

where:

• 273.1 + (temperature in °C) = absolute temperature in °K

• 2.8808 = log10(760 mm Hg)

• conversion factor for mm Hg to kPa is 0.133 (760 mm Hg = 101.325 kPa)

 

first approximation of boiling temperature in °C =

= (temperature in °C where boiled) + (estimated delta temperature)

 

Since the entropy of vaporization at the boiling point under standard pressure will be different than at the current temperature, the entropy of vaporization at the estimated boiling temperature needs to be calculated.

 

entropy of vaporization at 760 mm Hg and estimated boiling temperature =

= ((slope for group) * (first approximation for boiling temperature)) + (intercept for group)

 

corrected delta temperature =

= (initial estimate for delta temperature) * ((initial entropy estimate) / (entropy estimate at estimated boiling point))

 

second approximation of boiling temperature in °C =

= (current temperature in °C) + (corrected delta temperature)