At low pressures, volume V is very large and hence the correction term b (volume correction term) can be neglected in comparison to very large value of V. Thus, the van der Waals equation for 1 mole of a real gas.
\(\big(p+\frac{a}{V^2}\big)(V-b)\)RT may be written as
\(\big(p+\frac{a}{V^2}\big)(V)\) = RT
Or PV + \(\frac{a}{V}\) = RT
PV = RT - \(\frac{a}{V}\)
For large V (at very low pressure),\(\frac{a}{V}\) is very small and can be ignored.
\(\therefore\) PV becomes RT at very low pressure. That is why at very low pressure, real gases obey ideal gas equation.
