Question

A real gas obeying van der Waal equation will resemble ideal gas if the

• A. constants a and b are negligibly small
• B. a is large and b is small
• C. a is small and b is large
• D. constants a and b are large

Answer 1

The correct option is A constants a and b are negligibly small

According to van der Waal's equation $(P+\frac{a}{V^2})(V-b)=RT$ for one mole of the gas. Obviously if a and b are small, $\frac{a}{V^2}$ and $b$ can be neglected as compared to $P$ and $V$ and the equation reduces to $PV=RT$ for one mole of gas.
$\therefore$ A real gas will resemble an ideal gas when constant a and b are small