Answer:
The reaction referred to in this question is likely the reaction between hydrated copper(II) sulfate and anhydrous copper(II) sulfate, where the former is blue and the latter is white.
When the blue solution of hydrated copper(II) sulfate is exposed to moist air, it slowly turns white as water is absorbed, forming anhydrous copper(II) sulfate. This reaction is exothermic, meaning it releases heat, and is reversible. The reverse reaction occurs when anhydrous copper(II) sulfate is exposed to water vapor in the air, forming hydrated copper(II) sulfate and releasing heat.
In coastal areas, the humidity in the air tends to increase before a storm, which can trigger the reverse reaction between anhydrous copper(II) sulfate and water vapor. This releases heat, causing the weather-forecasting device to warm up, indicating that rain may be on the way.
Therefore, the observation of the blue solution turning white in the lab, which indicates the reversible reaction between hydrated copper(II) sulfate and anhydrous copper(II) sulfate, can indirectly indicate the presence of moisture in the air and the possibility of rain, similar to the process in weather-forecasting devices.