Pressure changes, isothermal

State function change General expression Approximate expression Ideal gas for liquid or solid 

In various applications, we will need expressions for the effect of changing the pressure at constant temperature on the internal energy, enthalpy, entropy, and Gibbs energy of a phase. We obtain the expressions by integrating expressions found in Table 7.1. For example. At/ is given by / (dU/dp)r P- The results are listed in the second column of Table 7.4. 

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Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

Changes in pressure at constant temperature. For a species undergoing an isothermal pressure change, AP,... 

CHAPTER 7 PURE SUBSTANCES IN SINGLE PHASES 7.6 ISOTHERMAL PRESSURE CHANGES... 

Table 7.4 Changes of state functions during an isothermal pressure change in a closed, single-phase system...

With the approximations that V, a, and kt are constant during an isothermal pressure change, and that ktP is negligible compared with aT,we obtain the expressions in the last column of Table 7.4. 

Suppose we want to use a reference state for solute B based on concentration. Because the isothermal pressure change involves a small change of volume, Cb changes slightly during the process, so that the right side of Eq. 9.7.14 is not quite the correct expression for - Vc,B-... 

Isothermal pressure change ideal gas, constant 7), Af/= 0, (Boyle s Law) = P2V2, and... 

We can also derive an expression for AS for an isothermal pressure change, using another Maxwell relation ... 

Derive the expression for the entropy change for an isothermal pressure change of a gas described by this truncated pressure virial equation of state. 

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