Date: 18 Aug 2003
To: axdstev@staff.uiuc.edu
Subject: Comments on your book "Chemical Principles" (2002)


Dear Professor Zumdahl,

I have three comments to your excellent textbook on Chemical Principles.

1. page 199. When defining the activity you set p_reference = 1 atm (exactly). However, this is the old convention, and
since 1982 the IUPAC standard (reference) pressure is 1 bar. Most thermodynamic data (e.g. Delta G) are now given at 1 bar, e.g.
see SI Chemical Data.

2. page 353. On page 141 you define an ideal gas as a gas that follows the ideal gas law pV=nRT. I agree.
However, on page 353-354 you say that for an ideal gas C_v = 3/2 R. This is not correct unless you change the definition of an ideal gas
to be a  monoatomic gas obeying pV=nRT. 
The confusion enters from kinetic gas theory which you use in Chapter 5 to derive the ideal gas law. 
However, even though your derivation may be restricted to a monoatomic gas, it does not mean that the ideal gas law itself is. 
In summary, ideal gases generally have heat capacities different from 3/2 R. 
In fact, most engineering calculations are based correlations for "ideal gas heat capacities" as a function of T. 

3. page 687. Your definition of the rate is that it is  "the change in concentration of a reactant or product per unit of time".
However, this  only applies if you consider a closed system (beaker) and also assume that the volume is constant.
As a counterexample, consider a cell (an open system) where there is a continuos transfer of feed (oxygen + sugar) to products (CO2 + water + energy), but
with a (approximately) constant concentration of all products and reactants. Obviously, the reaction rate is nonzero.    

The correct (general) definition is that the rate is "the change in number of moles of a reactant or product per unit of volume and per unit of time".

Best regards,
Sigurd Skogestad
Professor of Chemical Engineering
NTNU
Trondheim, Norway


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Reply:
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From: "Prof. Steve Zumdahl" <zumdahl@scs.uiuc.edu> 
Date: Tue, 19 Aug 2003 08:46:35 -0500 (CDT) 
Subject: Re: Comments on your book 'Chemical Principles' (2002) 
To: <skoge@chemeng.ntnu.no> 


> Dear Professor Skogestad,


Thank you very much for the feedback on chmical Principles.  Your comments
are well taken and I will take them into account as we prepare the next
edition.

Thanks again,

Steve Zumdahl