Ncert Exercises & Solutions

The relation between pressure exerted by an ideal gas (p_ideal) and observed pressure (p_real) is given by the equation,

$p_{ideal} = p_{real} + \frac{{an}^{2}}{V^{2}}$

1. If pressure is taken in Nm^-2, number of moles in mol and volume in m³, calculate the unit of 'a'.

2. What will be the unit of 'a' when pressure is in atmosphere and volume in dm³?

Given that,

p_{ideal} = p_{real} + \frac{{an}^{2}}{V^{2}}

(i)

a = \frac{{pV}^{2}}{n^{2}}

If units of p

= {Nm}^{- 2},

units of V

= m^{3}

, units of n=mol

then, units of a

= \frac{{Nm}^{- 2} {(m^{3})}^{2}}{{(mol)}^{2}} = {Nm}^{4} {mol}^{- 2}

(ii) If units of p = atm, units of V

= {dm}^{3}

, units of n = mol

then, units of a

= \frac{{pV}^{2}}{n^{2}} = \frac{atm . {({dm}^{3})}^{2}}{{(mol)}^{2}} = atm {dm}^{6} {mol}^{- 2}