Thermodynamics: An Engineering Approach 8th Edition

Published by McGraw-Hill Education
ISBN 10: 0-07339-817-9
ISBN 13: 978-0-07339-817-4

Chapter 12 - Thermodynamic Property Relations - Problems - Page 682: 12-48

Answer

See explanation

Work Step by Step

The definition for the volume expansivity is $$ \beta=\frac{1}{v}\left(\frac{\partial v}{\partial T}\right)_P $$ The definition for the isothermal compressibility is $$ \alpha=-\frac{1}{v}\left(\frac{\partial v}{\partial P}\right)_T $$ According to the cyclic relation, $$ \left(\frac{\partial v}{\partial T}\right)_P\left(\frac{\partial P}{\partial v}\right)_T\left(\frac{\partial T}{\partial P}\right)_v=-1 $$ which on rearrangement becomes $$ \left(\frac{\partial v}{\partial T}\right)_P=-\left(\frac{\partial v}{\partial P}\right)_T\left(\frac{\partial P}{\partial T}\right)_v $$ When this is substituted into the definition of the volume expansivity, the result is $$ \begin{aligned} \beta & =-\frac{1}{v}\left(\frac{\partial v}{\partial P}\right)_T\left(\frac{\partial P}{\partial T}\right)_v \\ & =-\alpha\left(\frac{\partial P}{\partial T}\right)_v \end{aligned} $$
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