IIT-JEE 2008 · Paper 1 · Chemistry Q56

ChemistryMultiple correct+4 / -1Question 56 of 69

A gas described by van der Waals equation

behaves similar to an ideal gas in the limit of large molar volumes

behaves similar to an ideal gas in the limit of large pressures

is characterised by van der Waals coefficients that are dependent on the identity of the gas but are independent of the temperature

has the pressure that is lower than the pressure exerted by the same gas behaving ideally

Answer and worked solution

Official answer: A, C

(A) At large molar volume, $a/V_m^2\to0$ and $b\ll V_m$ : the equation becomes $PV_m=RT$ . True.
(B) At high pressure the molecular volume matters and the gas deviates strongly. False.
(C) $a$ and $b$ are characteristic constants of each gas and do not depend on temperature in the model. True.
(D) The van der Waals pressure is lower than ideal when attraction dominates but higher when the excluded volume dominates (high pressure), so this is not always true. The official key also accepts it (AC or ACD), taking the usual low-pressure picture.

(A), (C) (key: AC or ACD)

IIT-JEE 2008 · Paper 1, Chemistry question 56