Water to Acid vs Acid to Water

[chem geek]

The heat (enthalpy) of dilution for some acids is given in this link. 31.45% HCl is around 10 so the heat of dilution is roughly 10 kJ/mol. 38.5% Sulfuric acid, by comparison, has a heat of dilution of around 28 kJ/mol so substantially higher. This link calculates the temperature rise for a specific example of adding acid to water and explains why adding water to acid is not a good idea. It basically has the water heat up so much that it can boil and splatter, causing acid to be propelled with it risking getting splashed with concentrated acid.

[Anonymous [GDPR] European in the UK]

I like adding the acid slowly to the pool all the way round and letting it fume, I grab my air guitar and sing "Smoke on the water"