Which statements(s) is/are true?

Question

van der Waals equation: (P + n²a/V²)(V - nb) = nRT where a and b are van der Waals constants. Textbook states: The constant a relates to the number and distribution of electrons, which relates to the complexity of a particle and the strength of its interparticle attractions. The constant b relates to particle volume.

Which statement(s) is/are true?

I. Ideally, the molar volume of a gas is 22.414 L at 1 atm and 25°C

II. The van der Waals "a" is greater for SO2(g) than for He(g)

III. For most gases, the slope of the PV/Rt vs. P_ext plot is initially negative.

IV. The value of the van der Waals "b" is an indication of the strength of the intermolecular forces in the gas.

Please provide an explanation for which ones are true and/or why the other choices are false.

Answer 1

I, II, and III are true; IV is not.

I. 22.4 is the calculated (from PV = nRT, using STP for 1 mole) volume. Since PV = nRT is the Ideal Gas Law, then this is valid for an "ideal" gas.

II. Since "a" indicates the complexity of a particle and the intermolecular forces that particle displays, then considering SO₂ vs. He we find: 1) SO₂ is obviously more 'complex' than He (3 atoms vs. 1 per molecule and, 2) SO₂ is polar, leading to rather strong dipole-dipole im forces. He is non-polar.

III. Look it up in any text. It shows the initial slope for most gases is negative.

IV. is false as it basically contradicts the given info for what "a" and "b": are in the vdW equation.