Diluting acids by adding acid to water is safer than adding water to acid because the process of dissolving an acid in water is highly exothermic, meaning it releases a lot of heat. Adding water to a concentrated acid can generate so much heat that the solution may splash out, causing burns, and the glass container might even break due to excessive localized heating.
Here’s a more detailed explanation:
Exothermic Reaction:
When an acid dissolves in water, it releases energy in the form of heat. This is a common chemical process, especially with strong acids like sulfuric acid.
Water’s Large Heat Capacity:
Water has a high heat capacity, meaning it can absorb a large amount of heat without a significant temperature increase. Adding acid to water allows the water to absorb the heat, preventing the solution from becoming too hot and potentially boiling.
Safety Concerns:
If water is added to a concentrated acid, the initial high concentration of acid can lead to a rapid release of heat. This can cause the solution to boil and even erupt, potentially splashing hot acid and causing burns. It can also lead to localized heating that could crack the glass container.
Control and Safety:
By adding the acid to water slowly, with constant stirring, the heat release can be better controlled. The water can absorb the heat as it’s released, and the stirring helps to distribute the heat evenly and prevent localized hotspots.