Questions 7-9 refer to the following information. At 27°C, five identical rigid 2.0 L vessels are fi — States of Matter Chemistry Question

STEPS:

1. Identify the nature of the container: The problem specifies that Vessel 5 is a rigid, sealed 2.0 L container. Because the vessel is sealed, it behaves as a closed system, which means no matter (atoms) can enter or escape the system.
2. Identify the physical process occurring: At 27°C, the vessel contains $N_2(g)$ and a $0.050\text{ mol}$ sample of solid iodine, $\text{I}_2(s)$. When the container is heated to 127°C, the solid iodine absorbs heat and undergoes a physical phase change (sublimation), vaporizing completely into gaseous iodine, $\text{I}_2(g)$.
3. Apply the Law of Conservation of Mass: This fundamental chemical principle states that in any closed system, mass is conserved because atoms are neither created nor destroyed during physical or chemical processes. Therefore, even though the iodine has transitioned from a solid to a gas, the total number of nitrogen and iodine atoms inside the sealed vessel remains completely constant.
4. Determine the mass comparison: Because the quantity and identity of every single atom in the vessel have not changed, the total mass of the vessel and its contents at 127°C must be exactly the same as it was at 27°C. This confirms that Option B is the correct answer.

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WHY_OTHERS_WRONG:

• Option A is incorrect: This option claims the mass is less because the $\text{I}_2$ is now in the vapor phase. While a gas is less dense than a solid, the physical phase change does not decrease the number of atoms or their mass within a closed, sealed vessel.
• Option C is incorrect: This option suggests that the mass is greater because $\text{I}_2$ will react with $\text{N}_2$ to form $\text{NI}_3$. However, nitrogen gas possesses an exceptionally strong triple covalent bond and is chemically inert under these mild conditions, meaning no reaction occurs. Even if a chemical reaction did occur, the conservation of mass in a sealed vessel dictates that the total mass of the closed system would remain unchanged.
• Option D is incorrect: This option incorrectly claims that the mass is greater because heating the vessel has increased the internal pressure and given the particles a higher average kinetic energy. While temperature, pressure, and kinetic energy do increase upon heating, these macroscopic properties do not add atoms or mass to a sealed container. Mass is entirely independent of pressure and kinetic energy.