Why can you add acid into water but you can't add water to acid?

Question

A source would be helpful.

It's about lab safety.

Answer 1

Exotherm

The Gibbs energy can all happen at once providing delta T and the all to annoying Delta V.

Do not add water to acid while in the container because heat release may cause spattering. Containers of this material may be hazardous when empty since they retain product residues (vapors, liquid); observe all warnings and precautions listed for the product.

USDA - Never add Water to Acid, an extreme exothermic chemical reaction will occur.

Acid reacts violently with water and can spatter acid onto personnel.

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Answer 2

When acid and water are combined (in whatever order) the acid is diluted. This process for many acids is highly exothermic ie. produces a large amount of heat. This heat can cause the mixture to vaporise.
Now if water is poured into say concentrated sulphuric acid, at first contact large portions of the concentrated acid will vaporise, producing dense, irritant fumes which can severely harm the experimenter.
On the other hand if we do it around the other way and add the concentrated acid to a beaker of water, its the highly diluted acid in the beaker that will vaporise. This will not do much harm since it is so much weaker. In fact if we add the acid slowly, in small quantities and intermittently to give it time to cool off, very little heat will be generated, preventing vaporisation. This is the correct procedure for dilution of acids. Also chemists sometimes swirl the flask to ensure good mixing.

Answer 3

Adding a drop of water into a very hot oil in a frying pan will cause the drop of water to spater.
The same thing ha[ppens if you add a drop of water on pure acid it will eXplode. The Reason is that the acid is very concentrated and is very reactive..
Therefore if you add acid vey slowy in water the acid would have enough time to dilute into the solution since only a small amount at a time will cause it to disolve into the solution.
It very dangerous for some one to drop water in acid it could spater and blind you. Hence if one does not have enough training in chemistry should not play with acids.

Answer 4

If you add a drop of water to a concentrated acid, heat is generated and the water can "boil" causing splashing of an acid/water mixture. The acid is still very concentrated...1 drop of water in a lot of acid. The dilution of a very concentrated acid causes heat.

If you add a drop of concentrated acid to water, heat is generated but quickly dissipates and the water is now a very dilute acid...one drop acid in a lot of water.

"Do it as you "ought-er", add the acid to the water"