The pressure exerted by 1 mol of CO2 at 273 K is 34.98 atm. Assuming that volume occupied by CO2 molecules is negligible, the value of van der Waals' constant for attraction of CO2 gas is

P+aV2[V−b]=RT∴P+aV2V=RT or V2P−RTV+a=0V=+RT±R2T2−4Pa2PSince, V is constant at given P and T, V can have only one value or discriminant = 0.∴ R2T2=4Pa or a=R2T24P=(0.0821)2×(273)24×34.98=3.59 dm6 atm mol−2