The first condition is because If we did treat particles with having a volume then we would have to correct for the volume they are taking up. So the volume of a box V would need to be corrected for the small volume taken up by the particles. Similarly elastic collisions and neglection of inter molecular forces are considered as otherwise the pressure would need to be corrected. Inter molecular force interactions will accelerate/decelerate the molecules thus changing force (therefore pressure) applied to the edge of our box.

Van der Waals equation attempts to take these corrections into account:

$$ \ (P + a(n/V)^2) + ((V/n) - b ) = RT $$

Where a and b are the Van der Waals (correction) coefficients. Hope this helps :)

The first condition is because if we did treat particles as having a volume then we would have to correct for the volume they take up. So the volume $V$ of a box would need to be corrected for the small volume taken up by the particles.

Similarly, elastic collisions and neglecting of intermolecular forces are considered as otherwise the pressure would need to be corrected. Intermolecular force interactions will accelerate or decelerate the molecules thus changing force (and pressure) applied to the edge of our box.

Van der Waals equation attempts to take these corrections into account:

$$ \ (P + a(n/V)^2)((V/n) - b ) = RT $$

Where $a$ and $b$ are the Van der Waals (correction) coefficients. Hope this helps :)