Question

Using van der Waal's equation, calculate the constant 'a' (in atm litre${}^2$ mol${}^{-2}$), when two moles of a gas confined in a four-litre flask exerts a pressure of 11.0 atmosphere at a temperature of 300 K. The value of 'b' is 0.05 litre mol${}^{-1}$.
Write integer part only.

Answer 1

van der Waal's equation for n mole of gas is:

$[P+\frac{n^{2}a}{V^2}][V-nb]=nRT$

Given,

V=4 litre;

P=11.0 atm,

T=300 K; b=0.05 litre mol${}^{-1}$,

n=2

Thus, $[11+\frac{2^{2}a}{4^2}][4-2\times 0.05]=2\times 0.0821\times 300$

a=6.46 atm litre${}^2$ mol${}^{-2}$

and integer part of this is 6.