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In the van der Waals equation for real gases, the coefficients $a$ and $b$ are used as respective correction terms for pressure and volume in the ideal gas equation.

I want to know whether the van der Waals coefficients are independent of 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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