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In the van der Waals eqn. for real gases the coefficients a and b are used in the respective correction terms of pressure and volume wrt to ideal gas eqn.

Is the value of the van der Waals coefficients dependent or independent of the absolute temperature or not?

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    $\begingroup$ The "formal" constants are just that - constants. However one could certainly have a table of $a$ and $b$ values for different ranges of temperature and pressure. See wikipedia article real gas for other equations. en.wikipedia.org/wiki/Real_gas $\endgroup$ – MaxW Oct 10 '16 at 20:11
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The constants a and b in the Van der Waals equation are supposed to be independent of temperature. But it is important to remember that, even though the Van der Waals equation does a better job of approximating the behavior of real gases than the ideal gas law (over a larger range of parameter values), it too is just approximation that applies only over a limited range of values for the parameters.

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The van der waals constant can be directly obtained from the critical temperature and pressure. We have,

${a = \frac{27 R^2 T_c^2} {64 P_c}}$

${b = \frac{R T_c }{ 8 P_c}}$

Since, $T_c$ and $P_c$ are constants, we can conclude that the van der waals constants are really "constants."

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