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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.
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."
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.
