What is the risk of adding water to acid instead of the reverse?

Adding water to acid instead of adding acid to water is a critical safety guideline due to the exothermic reaction that occurs when acid is mixed with water. When water is introduced to a concentrated acid, it can cause the acid to heat rapidly and potentially boil. The resulting steam can create a violent reaction, causing the acid to splatter and pose significant risks of burns or other injuries.

This behavior is particularly pronounced with strong acids, such as sulfuric acid, which releases a large amount of heat upon dilution. If acid is added to water, it allows the heat generated during the mixing to dissipate gradually throughout the larger volume of water, minimizing the risk of splattering and violent reactions.

In summary, the risk associated with adding water to acid primarily stems from the potential for a violent reaction due to rapid heating and steam production, emphasizing the importance of following proper procedures for safe handling and mixing of chemicals.