Question

The van der waals constant for $HCl$ are $a=371.843{\text{kPa.dm}}^6{\text{mol}}^{–2}$ and $b=40.8{\text{cm}}^3{\text{mol}}^{-1}$. Find the critical pressure of this substance.

• A. $8.3\text{Pa}$
• B. $8.3\text{MPa}$
• C. $3.2\text{atm}$
• D. $3.2\text{torr}$

Answer 1

The correct option is B $8.3\text{MPa}$

Given: $a=371.843kPad{m}^{6}mo{l}^{-2}=371.843\times {10}^{3}Pad{m}^{6}mo{l}^{-2}$

$b=40.8c{m}^{3}mo{l}^{-1}=40.8\times {10}^{-3}d{m}^{3}mo{l}^{-1}$

The critical pressure is given as,
$P_c=\frac{a}{27b^2}=\frac{371.843\times {10}^3}{27\times (40.8{)}^2\times {10}^{-6}}$$=\frac{371.843\times {10}^9}{27\times (40.8{)}^2}=8.273\times {10}^6\text{Pa}=8.273\text{MPa}$