When a bottle full of con. sulphuric acid is left opened in atmosphere, acid starts absorbing the moisture from the air.. when it absorbs moisture it's volume increases.. so it came out of the bottle

**The Behavior of Sulphuric Acid in the Atmosphere**

When a bottle filled with concentrated sulphuric acid is left open in the atmosphere, several factors come into play that can cause the acid to flow out of the bottle on its own. Here is a detailed explanation of this process:

**1. Chemical Nature of Sulphuric Acid:**
Sulphuric acid (H2SO4) is a highly corrosive and strong acid. It is known for its ability to react violently with various substances due to its acidic properties. Being a hygroscopic compound, it readily absorbs moisture from the surrounding environment.

**2. Absorption of Moisture:**
As the open bottle of sulphuric acid is exposed to the atmosphere, the acid begins to absorb moisture from the air. This absorption occurs through a process called hydration, where the acid molecules react with water molecules present in the air.

**3. Dilution of Sulphuric Acid:**
As sulphuric acid absorbs moisture, it starts to dilute itself. The water molecules that the acid absorbs gradually mix with the concentrated acid, leading to a decrease in the overall concentration of sulphuric acid in the bottle.

**4. Expansion of Volume:**
As the concentrated sulphuric acid dilutes itself, the volume of the liquid increases. This expansion is a result of the added water molecules, which occupy more space than the original acid molecules. The increased volume creates pressure inside the bottle.

**5. Pressure Build-Up:**
The pressure inside the bottle increases due to the expansion of volume caused by the dilution of sulphuric acid. The pressure build-up can become significant, especially if the bottle is tightly sealed or if the dilution process occurs rapidly. This pressure can result in the acid flowing out of the bottle.

**6. Capillary Action:**
Capillary action is the ability of a liquid to flow against gravity in narrow spaces, such as through a small opening. The capillary action of dilute sulphuric acid, combined with the pressure build-up, can cause the acid to flow out of the bottle. It will follow the path of least resistance, typically through the open neck of the bottle.

**7. Reactive Properties:**
Sulphuric acid is highly reactive with numerous substances. If any reactive materials, such as metals or organic compounds, are present in the vicinity of the open bottle, the acid may react with them, further exacerbating the flow of acid out of the bottle.

Overall, the combination of absorption of moisture, dilution, expansion of volume, pressure build-up, capillary action, and reactivity of sulphuric acid contribute to the acid flowing out of the bottle when left open in the atmosphere.