Question

Using Van der Waals equation $[P+\frac{a}{V^2}](V-b)=RT$, the term that accounts for effective volume in the Van der Waals equation for non-ideal gas is :

• A. $RT$
• B. $V-b$
• C. $[P+\frac{a}{V^2}]$
• D. $R{T}^{-1}$

Answer 1

The correct option is B $V-b$

In the ideal equation, $P_i{V}_i=nRT,V_i$ represents the ideal volume where the molecules can move freely.

In real gases, a part of the total volume is occupied by the gas molecules. Hence the free volume $V_i$ is the total volume $V$ minus the volume occupied by the gas molecules.

i.e. the real volume of gas= Actual volume of the container- volume occupied by $N$ molecules in motion.

$Vi=V-b$ for one mole of gas

$V_i=V-nb$ for $n$ mole of gas

Where $b$ is termed the 'excluded volume' or 'co-volume'.

It is constant and characteristic for each gas.

Hence, option B is correct.