2 replies to this topic

[ChemEngStudent17]

Hi All,

 

I'm looking at Coulson & Richardson Vol. 6, (3Rd Edition)  in Ch11, example 11.9 on page 535...there is an enthalpy relationship for simple hydrocarbons (taken from the book of Hydrocarbons, 1962).

The nomenclature states Hi and hi as specific enthalpy of vapour phase and liquid phase respectively but, I'm not entirely sure to which enthalpy is this relationship referring to (vaporization, formation, etc.)...and since all my components are aromatics it makes it confusing to look it up in other literature...

Your answers are  much appreciated!

Many Thanks,in advance!

[Art Montemayor]

I believe Coulson & Richardson is a work by British authors primarily used in Great Britain - and perhaps some of its ex-colonies.  I don’t have a copy of this work, but I think I have an idea of what you are faced with.

 

I think you are getting a bit mixed up with what you define as “enthalpy”.  Enthalpy is a specific measure of heat content and, as such, a measure of the heat content in a fluid at a specific condition of pressure and temperature.  Yet, you mention the heat of vaporization and the heat of formation - both increments of heat requirements and not specific heat contents.  Aren’t you getting your apples mixed up with oranges?

 

In other words, enthalpy is the heat content of a substance calculated from some stated base condition.  If you are seeking the heat of vaporization, then you simply subtract the enthalpy of the saturated liquid from the enthalpy of the saturated vapor resulting from the same liquid.  Of course, there is a phase change to consider.

 

I don’t see the confusion you report.

[ChemEngStudent17]

Adding to my post above, the units reported in the book are those for enthalpy kJ/kmol (SI) and not those for specific heat capacity kJ/mol*K, hence the confusion as to what the book refers to as specific enthalpy of vapor and specific heat of liquid??

Edited by ChemEngStudent17, 25 July 2017 - 04:34 AM.