The best explanation for the lower pressure in container 4 is that SO2 molecules — States of Matter Chemistry Question

STEPS:

1. Recall the conditions of the containers: Under ideal gas behavior, equal moles of any gas in identical rigid vessels at the same temperature must exert the exact same pressure. Containers 1, 2, and 3 all contain approximately 1.0 mole of gas and exert a pressure of $2.00\text{ atm}$. Container 4 contains exactly 1.0 mole of sulfur dioxide ($\text{SO}_2$, mass of $64.1\text{ g}$ with a molar mass of $\approx 64.1\text{ g/mol}$) but exerts a slightly lower pressure of $1.96\text{ atm}$.
2. Understand the cause of real gas deviations: The Ideal Gas Law assumes that gas particles experience no intermolecular attractions. In real gases, however, intermolecular attractive forces (IMFs) exist between molecules.
3. Analyze how intermolecular attractions affect gas pressure: When real gas molecules attract one another, they are pulled slightly toward each other and away from the container walls. This reduces both the frequency and the force of their collisions with the walls, causing the measured pressure to be lower than the ideal pressure predicted by the Ideal Gas Law.
4. Compare the intermolecular forces of the four gases:
* Helium ($\text{He}$) and Neon ($\text{Ne}$) are small, nonpolar noble gas atoms with extremely weak London dispersion forces (LDFs).
* Methane ($\text{CH}_4$) (the gas in Container 3) is a highly symmetric, nonpolar tetrahedral molecule that also only exhibits relatively weak LDFs.
* Sulfur Dioxide ($\text{SO}_2$) is an asymmetric, bent, highly polar molecule with a large, polarizable electron cloud. It experiences strong dipole-dipole attractions in addition to significantly stronger LDFs compared to the other three gases.
5. Formulate the final conclusion: Because $\text{SO}_2$ molecules have much stronger intermolecular attractions than the other three gases, they pull toward one another more strongly. This decreases the impact force of the molecules against the container walls, resulting in the observed lower pressure of $1.96\text{ atm}$. This makes Option C the correct answer.

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WHY_OTHERS_WRONG:

• A is incorrect: As established in Question 15, because $\text{SO}_2$ has the highest molar mass among the gases, its molecules actually have the smallest average speed, not the largest. Furthermore, a larger average speed would lead to more frequent and forceful collisions, which would increase pressure, not decrease it.
• B is incorrect: If the physical volume occupied by the gas molecules themselves was the dominating factor (representing a deviation from the ideal gas assumption of negligible particle volume), the free volume available for the molecules to move would be reduced. This would cause the real gas to collide with the walls *more* frequently, resulting in a higher pressure than ideal, not a lower pressure.
• C is correct: See the steps above.
• D is incorrect: Although $\text{SO}_2$ contains $\pi$ bonds (due to double bond resonance structures) and gases like $\text{He}$ and $\text{Ne}$ contain no bonds, this is an intramolecular property (bonding within the individual molecule). It is the intermolecular attractions (forces *between* separate molecules) that govern gas-phase pressure deviations.