What will be the pressure exerted by a mixture of 3.2 g of methane and 4.4 g of carbon dioxide contained in a 9 d${\mathrm{m}}^3$  flask at 27°C?

$\text{ Moles of }{\mathrm{CH}}_4\text{, }$

${\mathrm{n}}_{{\mathrm{CH}}_4}=\frac{\text{ Mass of }{\mathrm{CH}}_4}{\text{ Molar mass of }{\mathrm{CH}}_4}$

$\left[\text{ Molar mass of }{\mathrm{CH}}_4=12+4\times 1=16\right.\text{ ]}$

$=\frac{3.2}{16}=0.2 \mathrm{mol}$

$\text{ Similarly, moles of }{\mathrm{CO}}_2\text{, }$

$n_{{\mathrm{CO}}_2}=\frac{4.4}{44}=0.1 \mathrm{mol}$

$\left[\text{ Molar mass of }{\mathrm{CO}}_2=12+2\times 16=44\right]$

Total moles = 0.2 + 0.1 = 0.3 mol

$\mathrm{p} \mathrm{V}=\mathrm{n} \mathrm{R} \mathrm{T}$

$\mathrm{p}=\frac{\mathrm{nRT}}{\mathrm{V}}$

$\mathrm{p}=\frac{0.3 \mathrm{mol}\times 0.0821{\mathrm{dm}}^3 \mathrm{atm}{ \mathrm{K}}^{-1}{ \mathrm{mol}}^{-1}\times 300 \mathrm{K}}{9{\mathrm{dm}}^3}$

= 0.821atm

In terms of SI units

$\text{ Pressure, }\mathrm{p}=\frac{0.3 \mathrm{mol}\times 8.314 \mathrm{Pa}{ \mathrm{m}}^3{ \mathrm{K}}^{-1}{ \mathrm{mol}}^{-1}\times 300}{9\times {10}^{-3}{ \mathrm{m}}^3}$

$p=8.314\times {10}^4 \mathrm{Pa}$