By what magnitude would the pressure exterted by water on the walls of the vessel have increased if the intermolecular attraction forces had vanished ?

Explanation

From the Vander Waals equation
`p = (RT)/(V - b) -(a)/(V^2)`
where `V` = Volume of one `gm` mole of the substances.
For water `V = 18 c.c` per mole `= 1.8 xx 10^-2` litre per mole
`a = 5.47 "atoms".(litre^2)/("mole"^2)`
If molecular attraction vanished the equation will be
`p' (RT)/(V - b)`
for the same specific volume. Thus
`Delta p = (a)/(V^2) = (5.47)/(1.8 xx 1.8) xx 10^4 "atoms" ~~ 1.7 xx 10^4` atoms.