Final answer:
The gas accumulated in the vials is nitrogen dioxide (NO2), responsible for the brown color. Changes in pressure can alter the equilibrium between colorless N2O4 and brown NO2, resulting in a visible color change. Additionally, warmer water saturated with CO2 can release the gas when it reaches the lake's surface.
Step-by-step explanation:
The gas that accumulated in the vials during the chemical reaction was nitrogen dioxide (NO2), which is known for its brown color. The color change of the dye can be attributed to the chemical equilibrium of N2O4 and NO2. As the equilibrium shifts, the concentration of the gases changes, affecting the color observed. For instance, a decrease in pressure increases the volume of the gas and reduces its concentration, leading to a lighter color as the equilibrium favors the colorless N2O4. However, as pressure increases, causing a decrease in volume, the concentration of the gas increases, the color becomes darker, and the equilibrium shifts towards the production of more NO2 molecules.
Regarding the lake turnover scenario, the gradual heating resulted in the rise of warmer water that was high in carbon dioxide (CO2), eventually reaching the surface and releasing large quantities of CO2 into the air. This colorless gas flowed into the valley and affected the inhabitants. In another situation, when different gases are present, they absorb specific wavelengths of light, resulting in a spectrum with dark lines characteristic of those elements, which is crucial in the field of astronomy.