# Van der Waals equation

The van der Waals equation (or van der Waals equation of state; named after Johannes Diderik van der Waals) is an equation of state that generalizes the ideal gas law based on plausible reasons that real gases do not act ideally.

$\left(P+a\dfrac{1}{V_m^2}\right)(V_m-b)=RT$

where $$a$$ is a constant whose value depends on the gas, $$b$$ is the volume that is occupied by one mole of the molecules, $$V_m$$ is the molar volume of the gas, $$R$$ is the universal gas constant, $$T$$ is temperature, $$P$$ is pressure.

$a=\dfrac{27R^2T_c^2}{64p_c}$

$b=\dfrac{RT_c}{8p_c}$

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