Final answer:
The color change from colorless to brown in the vial indicates the accumulation of NO₂ gas due to a shift in the equilibrium towards the product side. This is a result of changing gas concentrations and pressures, explained by gas laws and chemical equilibrium principles.
Step-by-step explanation:
The gas accumulated in the vial is likely NO₂, based on the equilibrium reaction between colorless N₂O₄ and brown NO₂ gas (N₂O₄(g, colorless) ⇒ 2NO₂(g, brown)).
If the color of the dye changed from colorless to brown, it suggests a shift in the equilibrium toward the product, NO₂, which has a brown color.
The change in color can be directly linked to the change in the concentration of the gases within the syringe: a decrease in pressure, due to an increase in volume, leads to a lighter color initially, indicating a lower concentration of NO₂. Then, as the equilibrium adjusts to relieve stress, the concentration of NO₂ increases and the color turns darker.
When investigating the behavior of gases and their interactions with color-changing substances, it's essential to understand the principles of gas laws and chemical equilibrium. Such knowledge explains why the color of a dye may change in response to variations in gas concentration and pressure. When the equilibrium shifts towards producing more NO₂, the result is observable through a visually darker hue.