In an experiment, Ann mixes concentrated sulfuric acid with water in a reaction test tube. The walls of the test tube turn hot. What type of reaction has occurred

Answer: I hope Ann got the order of addition right! Always add acid to water. An hydration reaction has occurred.

Explanation: Upon addition to water concentrated acids become hydrated, and both anion and cation become solvated by water molecules to form H3O + (aq) and SO2-4 (aq), each aquated by (solvated by) water molecules. Because bonds are formed between water and H + this reaction is reasonably exothermic and releases heat.

The addition of water to acid results in local heating of the added water. The acid would spit at you. (If you spit in acid it spits back!).